Add a short delay to action dispatches

delay.diff

diff --git a/src/sidebar/store/index.js b/src/sidebar/store/index.js
index 8051a738..1e725db5 100644
--- a/src/sidebar/store/index.js
+++ b/src/sidebar/store/index.js
@@ -71,6 +71,33 @@ function angularDigestMiddleware($rootScope) {
   };
 }
 
+/**
+ * Middleware which adds an artificial delay to all actions going through
+ * the store. This is a debugging aid which makes it easier to observe
+ * short-lived states.
+ *
+ * @param {number} delay - Delay in milliseconds.
+ */
+function delayMiddleware(delay) {
+  const queue = [];
+  return next => {
+    function dispatchNextAction() {
+      const action = queue.shift();
+      next(action);
+      if (queue.length > 0) {
+        setTimeout(dispatchNextAction, delay);
+      }
+    }
+
+    return action => {
+      queue.push(action);
+      if (queue.length === 1) {
+        setTimeout(dispatchNextAction, delay);
+      }
+    };
+  };
+}
+
 /**
  * Factory which creates the sidebar app's state store.
  *
@@ -82,6 +109,7 @@ function angularDigestMiddleware($rootScope) {
 // @ngInject
 function store($rootScope, settings) {
   const middleware = [
+    delayMiddleware.bind(null, 300 /* delay */),
     debugMiddleware,
     angularDigestMiddleware.bind(null, $rootScope),
   ];