Android - Completely transparent status bar.

activity_transparent_status_bar.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.DrawerLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/drawer"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:context=".ui.demo.TransparentStatusBarActivity"
    tools:openDrawer="end">

    <android.support.design.widget.CoordinatorLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:fitsSystemWindows="true">

        <include layout="@layout/toolbar" />

        <android.support.v7.widget.RecyclerView
            android:id="@+id/recycler"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:scrollbars="none"
            app:layout_behavior="@string/appbar_scrolling_view_behavior" />

    </android.support.design.widget.CoordinatorLayout>

    <android.support.design.widget.NavigationView
        android:id="@+id/nav"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="end"
        android:fitsSystemWindows="true"
        app:headerLayout="@layout/nav_header_main"
        app:menu="@menu/nav_menu_main" />

</android.support.v4.widget.DrawerLayout>

TransparentStatusBarActivity.java

package cc.cubone.turbo.ui.demo;

import android.content.Context;
import android.graphics.Color;
import android.os.Build;
import android.os.Bundle;
import android.os.PersistableBundle;
import android.support.annotation.ColorInt;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBar;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.view.Window;
import android.view.WindowManager;

import cc.cubone.turbo.R;
import cc.cubone.turbo.core.rom.MIUIUtils;

public class TransparentStatusBarActivity extends AppCompatActivity {

    private DrawerLayout mDrawerLayout;
    private ActionBarDrawerToggle mDrawerToggle;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_transparent_status_bar);

        Toolbar toolbar = (Toolbar) findViewById(R.id.bar);
        setSupportActionBar(toolbar);

        // Set the back arrow in the action bar
        ActionBar actionBar = getSupportActionBar();
        if (actionBar != null) {
            actionBar.setDisplayHomeAsUpEnabled(true);
            actionBar.setHomeButtonEnabled(false);
        }

        initDrawer(toolbar);
        initStatusBar(toolbar);
    }

    @Override
    public void onPostCreate(Bundle savedInstanceState, PersistableBundle persistentState) {
        super.onPostCreate(savedInstanceState, persistentState);
        if (mDrawerToggle != null) mDrawerToggle.syncState();
    }

    private void initDrawer(Toolbar toolbar) {
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer);
        if (drawer != null) {
            // slide drawer from right to left
            //((DrawerLayout.LayoutParams) drawer.getChildAt(1).getLayoutParams()).gravity = GravityCompat.END;
            ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                    this, drawer, null, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
            drawer.setDrawerListener(toggle);
            toggle.setDrawerIndicatorEnabled(false);
            toggle.syncState();
            mDrawerToggle = toggle;
        }
        mDrawerLayout = drawer;
    }

    protected void initStatusBar(View toolbar) {
        // Ensure `setStatusBarImmersiveMode()`
        if (Build.VERSION.SDK_INT >= 19) { // 19, 4.4, KITKAT
            // Ensure content view `fitsSystemWindows` is false.
            ViewGroup contentParent = (ViewGroup) findViewById(android.R.id.content);
            View content = contentParent.getChildAt(0);
            // If using `DrawerLayout`, must ensure its subviews `fitsSystemWindows` are all false.
            // Because in some roms, such as MIUI, it will fits system windows for each subview.
            setFitsSystemWindows(content, false, true);

            // Add padding to hold the status bar place.
            clipToStatusBar(toolbar);

            // Add a view to hold the status bar place.
            // Note: if using appbar_scrolling_view_behavior of CoordinatorLayout, however,
            // the holder view could be scrolled to outside as it above the app bar.
            //holdStatusBar(toolbar, R.color.colorPrimary);
        }
    }

    protected void setFitsSystemWindows(View view, boolean fitSystemWindows, boolean applyToChildren) {
        if (view == null) return;
        view.setFitsSystemWindows(fitSystemWindows);
        if (applyToChildren && (view instanceof ViewGroup)) {
            ViewGroup viewGroup = (ViewGroup) view;
            for (int i = 0, n = viewGroup.getChildCount(); i < n; i++) {
                viewGroup.getChildAt(i).setFitsSystemWindows(fitSystemWindows);
            }
        }
    }

    protected void clipToStatusBar(View view) {
        final int statusBarHeight = getStatusBarHeight(this);
        view.getLayoutParams().height += statusBarHeight;
        view.setPadding(0, statusBarHeight, 0, 0);
    }

    /*protected void holdStatusBar(View view, @ColorRes int resid) {
        ViewGroup toolbarParent = (ViewGroup) view.getParent();
        int i = 0;
        for (int n = toolbarParent.getChildCount(); i < n; i++) {
            if (toolbarParent.getChildAt(i) == view) break;
        }
        View holderView = new View(this);
        holderView.setId(R.id.status_bar);
        holderView.setBackgroundColor(getResources().getColor(resid));
        toolbarParent.addView(holderView, i, new ViewGroup.LayoutParams(
                ViewGroup.LayoutParams.MATCH_PARENT, getStatusBarHeight(this)));
        if (toolbarParent instanceof RelativeLayout) {
            ((RelativeLayout.LayoutParams) toolbarParent.getLayoutParams())
                    .addRule(RelativeLayout.BELOW, R.id.status_bar);
        }
    }*/

    protected int getStatusBarHeight(Context context) {
        int result = 0;
        int resourceId = context.getResources().getIdentifier("status_bar_height", "dimen", "android");
        if (resourceId > 0) {
            result = context.getResources().getDimensionPixelSize(resourceId);
        }
        return result;
    }

    protected void setStatusBarImmersiveMode(@ColorInt int color) {
        Window win = getWindow();

        // StatusBar
        if (Build.VERSION.SDK_INT >= 19) { // 19, 4.4, KITKAT
            win.addFlags(WindowManager.LayoutParams.FLAG_TRANSLUCENT_STATUS);
        }
        if (Build.VERSION.SDK_INT >= 21) { // 21, 5.0, LOLLIPOP
            win.getAttributes().systemUiVisibility |=
                    (View.SYSTEM_UI_FLAG_LAYOUT_STABLE
                            | View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN);
            win.clearFlags(WindowManager.LayoutParams.FLAG_TRANSLUCENT_STATUS);
            win.addFlags(WindowManager.LayoutParams.FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS);
            win.setStatusBarColor(color);
        }

        // Setup immersive mode on third-party rom
        if (Build.VERSION.SDK_INT >= 19) { // 19, 4.4, KITKAT
            //FlymeUtils.setStatusBarDarkIcon(win, false);
            MIUIUtils.setStatusBar(win, MIUIUtils.StatusBarMode.TRANSPARENT);
        }
    }

    @Override
    public void onAttachedToWindow() {
        super.onAttachedToWindow();
        setStatusBarImmersiveMode(Color.TRANSPARENT);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        if (mDrawerLayout != null) {
            getMenuInflater().inflate(R.menu.transparent_status_bar, menu);
        }
        //TintUtils.tintList(this, menu, R.color.bar_icon_color);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case android.R.id.home: finish(); return true;
            case R.id.action_menu: toggleDrawer(GravityCompat.END); return true;
            default: return super.onOptionsItemSelected(item);
        }
    }

    @Override
    public void onBackPressed() {
        if (isDrawerOpen(GravityCompat.END)) {
            toggleDrawer(GravityCompat.END);
        } else {
            super.onBackPressed();
        }
    }

    @Override
    public void finish() {
        super.finish();
        overridePendingTransition(R.anim.slide_in_left, R.anim.slide_out_right);
    }

    private boolean isDrawerOpen(int drawerGravity) {
        return mDrawerLayout != null && mDrawerLayout.isDrawerOpen(drawerGravity);
    }

    private void toggleDrawer(int drawerGravity) {
        if (mDrawerLayout == null) return;
        if (mDrawerLayout.isDrawerVisible(drawerGravity)) {
            mDrawerLayout.closeDrawer(drawerGravity);
        } else {
            mDrawerLayout.openDrawer(drawerGravity);
        }
    }

}

Related: MIUIUtils.java

Works perfectly. Thanks @joinAero