Bug 1561227 Part 2: Define and fire an internal event when BrowserChild has finished resizing. r=botond,emilio

This event is useful for tests that resize the RDM pane and need to
know when all resolution adjusting effects are complete.

Differential Revision: https://phabricator.services.mozilla.com/D47364

--HG--
extra : moz-landing-system : lando

dom/ipc/BrowserChild.cpp

@@ -16,6 +16,7 @@
 #include "BrowserParent.h"
 #include "js/JSON.h"
 #include "mozilla/Preferences.h"
+#include "mozilla/AsyncEventDispatcher.h"
 #include "mozilla/BrowserElementParent.h"
 #include "mozilla/ClearOnShutdown.h"
 #include "mozilla/EventListenerManager.h"
@@ -1262,6 +1263,18 @@ mozilla::ipc::IPCResult BrowserChild::RecvUpdateDimensions(
                         screenRect.y + mClientOffset.y + mChromeOffset.y,
                         screenSize.width, screenSize.height, true);
 
+  // For our devtools Responsive Design Mode, we need to send a special
+  // event to indicate that we've finished processing a frame size change.
+  // This is used by RDM to respond correctly to changes to full zoom,
+  // which also change the window size.
+  RefPtr<Document> doc = GetTopLevelDocument();
+  if (doc && doc->InRDMPane()) {
+    RefPtr<AsyncEventDispatcher> dispatcher = new AsyncEventDispatcher(
+        doc, NS_LITERAL_STRING("mozupdatedremoteframedimensions"),
+        CanBubble::eYes, ChromeOnlyDispatch::eYes);
+    dispatcher->PostDOMEvent();
+  }
+
   return IPC_OK();
 }