Bug 863702 - [B2G] :active state is sometime not rendered if you tap quickly. r=fabrice

dom/browser-element/BrowserElementPanning.js

@@ -24,10 +24,16 @@ const ContentPanning = {
   hybridEvents: false,
 
   init: function cp_init() {
+    let els = Cc["@mozilla.org/eventlistenerservice;1"]
+                .getService(Ci.nsIEventListenerService);
+
     var events;
     try {
       content.document.createEvent('TouchEvent');
       events = ['touchstart', 'touchend', 'touchmove'];
+      els.addSystemEventListener(global, 'mousedown',
+                                 this.handleEvent.bind(this),
+                                 /* useCapture = */ true);
       this.watchedEventsType = 'touch';
 #ifdef MOZ_WIDGET_GONK
       // The gonk widget backend does not deliver mouse events per
@@ -49,9 +55,6 @@ const ContentPanning = {
     // it will handle subframe scrolling too. We don't need to listen for
     // these events.
     if (!this._asyncPanZoomForViewportFrame) {
-      let els = Cc["@mozilla.org/eventlistenerservice;1"]
-                  .getService(Ci.nsIEventListenerService);
-
       events.forEach(function(type) {
         // Using the system group for mouse/touch events to avoid
         // missing events if .stopPropagation() has been called.
@@ -80,6 +83,24 @@ const ContentPanning = {
 
     switch (evt.type) {
       case 'mousedown':
+        // Touch events will generate a quick sequence of mouse events
+        // (mousemove, mousedown, mouseup) right after touchend. But
+        // the :active pseudo state is set during mousedown and is
+        // cleared during mouseup. The above code will delay the
+        // mouseup for a small amount of ms.
+        if (this.watchedEventsType == 'touch' && !this.hybridEvents) {
+          this._setActive(evt.target);
+
+          var start = Date.now();
+          var thread = Services.tm.currentThread;
+          while ((Date.now() - start) < 100) {
+            thread.processNextEvent(true);
+          }
+
+          // Don't consider this mousedown as the beginning of a
+          // panning sequence and just bail out.
+          return;
+        }
       case 'touchstart':
         this.onTouchStart(evt);
         break;