Don't schedule an animation during compositing dirty-bit setting unless needed.

Source/core/page/PageAnimator.cpp

Index: Source/core/page/PageAnimator.cpp
diff --git a/Source/core/page/PageAnimator.cpp b/Source/core/page/PageAnimator.cpp
index 8bca069bd0b727cada442ae55655b1278ca97414..c2255481bb51838a961950b138e3f22151e50ae0 100644
--- a/Source/core/page/PageAnimator.cpp
+++ b/Source/core/page/PageAnimator.cpp
@@ -20,6 +20,7 @@ PageAnimator::PageAnimator(Page* page)
     : m_page(page)
     , m_animationFramePending(false)
     , m_servicingAnimations(false)
+    , m_updatingLayoutAndStyleForPainting(false)
 {
 }
 
@@ -44,10 +45,29 @@ void PageAnimator::serviceScriptedAnimations(double monotonicAnimationStartTime)
 
 void PageAnimator::scheduleVisualUpdate()
 {
-    if (m_animationFramePending || m_servicingAnimations)
+    // FIXME: also include m_animationFramePending here. It is currently not there due to crbug.com/353756.
+    if (m_servicingAnimations || m_updatingLayoutAndStyleForPainting)
         return;
     m_page->chrome().scheduleAnimation();
-    ASSERT(m_animationFramePending);
+}
+
+void PageAnimator::updateLayoutAndStyleForPainting()
+{
+    RefPtr<FrameView> view = m_page->mainFrame()->view();
+
+    TemporaryChange<bool> servicing(m_updatingLayoutAndStyleForPainting, true);
+
+    // In order for our child HWNDs (NativeWindowWidgets) to update properly,
+    // they need to be told that we are updating the screen. The problem is that
+    // the native widgets need to recalculate their clip region and not overlap
+    // any of our non-native widgets. To force the resizing, call
+    // setFrameRect(). This will be a quick operation for most frames, but the
+    // NativeWindowWidgets will update a proper clipping region.
+    view->setFrameRect(view->frameRect());
+
+    // setFrameRect may have the side-effect of causing existing page layout to
+    // be invalidated, so layout needs to be called last.
+    view->updateLayoutAndStyleForPainting();
 }
 
 }