How Bowtie accomplishes a movable window with a WebView.

BTOverlayView.m

// BTOverlayView.h

@interface BTOverlayView : NSView {
    NSWindow *mainWindow;
	NSPoint initialLocation;
	NSTrackingArea *tArea;
	
	BOOL frameChanged;
}

@property(assign, readwrite) IBOutlet NSWindow *mainWindow;

- (void)mouseDragged:(NSEvent *)theEvent;
- (void)mouseDown:(NSEvent *)theEvent;
- (void)mouseUp:(NSEvent *)theEvent;

@end

// BTOverlayView.m

@implementation BTOverlayView

@synthesize mainWindow;

- (id)initWithFrame:(NSRect)rect
{
	if (self = [super initWithFrame:rect])
	{
		frameChanged = NO;
		tArea = [[NSTrackingArea alloc] initWithRect:rect options:NSTrackingMouseEnteredAndExited|NSTrackingActiveAlways|NSTrackingInVisibleRect owner:self userInfo:nil];
		[self addTrackingArea:tArea];
	}
	return self;
}

- (void)dealloc
{
	[tArea release];
	[super dealloc];
}

- (void)mouseDragged:(NSEvent *)theEvent
{
	if (![[NSUserDefaults standardUserDefaults] boolForKey:@"lockWindowPosition"])
	{
		NSPoint newOrigin;
		NSRect screenFrame = [[NSScreen mainScreen] frame];
		NSRect windowFrame = [mainWindow frame];
		
		NSPoint currentLocation = [mainWindow convertBaseToScreen:[mainWindow mouseLocationOutsideOfEventStream]];
		newOrigin.x = currentLocation.x - initialLocation.x;
		newOrigin.y = currentLocation.y - initialLocation.y;
		
		// Don't let window get dragged up under the menu bar
		if ((newOrigin.y + windowFrame.size.height) > (screenFrame.origin.y + screenFrame.size.height))
			newOrigin.y = screenFrame.origin.y + (screenFrame.size.height - windowFrame.size.height);
		
		//go ahead and move the window to the new location
		[mainWindow setFrameOrigin:newOrigin];
		frameChanged = YES;
	}
}

- (void)mouseDown:(NSEvent *)theEvent
{    
    // grab the mouse location in global coordinates
	initialLocation = [theEvent locationInWindow];
	
	[super mouseDown:theEvent];
}
- (void)mouseUp:(NSEvent *)theEvent
{
	if (frameChanged)
	{
	    // you could do something here to notify your theme that the window moved
	}
	
	frameChanged = NO;
	
	[super mouseUp:theEvent];
}

@end