Bug 876426. Part 1: Fire 'resizevideocontrols' event on video controls element when the element's size is changed. r=mattwoodrow

layout/generic/nsVideoFrame.cpp

@@ -234,6 +234,20 @@ nsVideoFrame::BuildLayer(nsDisplayListBuilder* aBuilder,
   return result.forget();
 }
 
+class DispatchResizeToControls : public nsRunnable
+{
+public:
+  DispatchResizeToControls(nsIContent* aContent)
+    : mContent(aContent) {}
+  NS_IMETHOD Run() {
+    nsContentUtils::DispatchTrustedEvent(mContent->OwnerDoc(), mContent,
+                                         NS_LITERAL_STRING("resizevideocontrols"),
+                                         false, false);
+    return NS_OK;
+  }
+  nsCOMPtr<nsIContent> mContent;
+};
+
 NS_IMETHODIMP
 nsVideoFrame::Reflow(nsPresContext*           aPresContext,
                      nsHTMLReflowMetrics&     aMetrics,
@@ -307,12 +321,17 @@ nsVideoFrame::Reflow(nsPresContext*           aPresContext,
     } else if (child->GetContent() == mVideoControls) {
       // Reflow the video controls frame.
       nsBoxLayoutState boxState(PresContext(), aReflowState.rendContext);
+      nsSize size = child->GetSize();
       nsBoxFrame::LayoutChildAt(boxState,
                                 child,
                                 nsRect(mBorderPadding.left,
                                        mBorderPadding.top,
                                        aReflowState.ComputedWidth(),
                                        aReflowState.ComputedHeight()));
+      if (child->GetSize() != size) {
+        nsRefPtr<nsRunnable> event = new DispatchResizeToControls(child->GetContent());
+        nsContentUtils::AddScriptRunner(event);
+      }
     } else if (child->GetContent() == mCaptionDiv) {
       // Reflow to caption div
       nsHTMLReflowMetrics kidDesiredSize;