Bug 1362382 - Move RegisterDragDrop to be called during idle time, if possible r=jimm

Additionally, do not call RegisterDragDrop for hidden windows.

MozReview-Commit-ID: Fv8j9FntGGT

view/nsView.cpp

@@ -716,7 +716,10 @@ nsresult nsView::AttachToTopLevelWidget(nsIWidget* aWidget)
   mWindow = aWidget;
 
   mWindow->SetAttachedWidgetListener(this);
-  mWindow->EnableDragDrop(true);
+  if (mWindow->WindowType() != eWindowType_invisible) {
+    nsresult rv = mWindow->AsyncEnableDragDrop(true);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
   mWidgetIsTopLevel = true;
 
   // Refresh the view bounds

widget/nsBaseWidget.cpp

@@ -125,6 +125,11 @@ int32_t nsIWidget::sPointerIdCounter = 0;
 /*static*/ uint64_t AutoObserverNotifier::sObserverId = 0;
 /*static*/ nsDataHashtable<nsUint64HashKey, nsCOMPtr<nsIObserver>> AutoObserverNotifier::sSavedObservers;
 
+// The maximum amount of time to let the EnableDragDrop runnable wait in the
+// idle queue before timing out and moving it to the regular queue. Value is in
+// milliseconds.
+const uint32_t kAsyncDragDropTimeout = 1000;
+
 namespace mozilla {
 namespace widget {
 
@@ -2229,6 +2234,18 @@ nsBaseWidget::UnregisterPluginWindowForRemoteUpdates()
 #endif
 }
 
+nsresult
+nsBaseWidget::AsyncEnableDragDrop(bool aEnable)
+{
+  RefPtr<nsBaseWidget> kungFuDeathGrip = this;
+  return NS_IdleDispatchToCurrentThread(
+    NS_NewRunnableFunction("AsyncEnableDragDropFn",
+                           [this, aEnable, kungFuDeathGrip]() {
+                             EnableDragDrop(aEnable);
+                           }),
+    kAsyncDragDropTimeout);
+}
+
 // static
 nsIWidget*
 nsIWidget::LookupRegisteredPluginWindow(uintptr_t aWindowID)

widget/nsBaseWidget.h

@@ -250,6 +250,7 @@ public:
   virtual nsresult        SetNonClientMargins(LayoutDeviceIntMargin& aMargins) override;
   virtual LayoutDeviceIntPoint GetClientOffset() override;
   virtual void            EnableDragDrop(bool aEnable) override {};
+  virtual nsresult        AsyncEnableDragDrop(bool aEnable) override;
   virtual MOZ_MUST_USE nsresult
                           GetAttention(int32_t aCycleCount) override
                           { return NS_OK; }

widget/nsIWidget.h

@@ -1415,6 +1415,7 @@ class nsIWidget : public nsISupports
      * Enables the dropping of files to a widget.
      */
     virtual void EnableDragDrop(bool aEnable) = 0;
+    virtual nsresult AsyncEnableDragDrop(bool aEnable) = 0;
 
     /**
      * Enables/Disables system mouse capture.

widget/windows/nsWindow.cpp

@@ -3772,7 +3772,10 @@ nsWindow::ClientToWindowSize(const LayoutDeviceIntSize& aClientSize)
 void
 nsWindow::EnableDragDrop(bool aEnable)
 {
-  NS_ASSERTION(mWnd, "nsWindow::EnableDragDrop() called after Destroy()");
+  if (!mWnd) {
+    // Return early if the window already closed
+    return;
+  }
 
   if (aEnable) {
     if (!mNativeDragTarget) {