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

Source/core/page/PageAnimator.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "core/page/PageAnimator.h"
 
 #include "core/animation/DocumentAnimations.h"
 #include "core/dom/Document.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
 #include "core/page/Chrome.h"
 #include "core/page/ChromeClient.h"
 #include "core/page/Page.h"
 #include "core/svg/SVGDocumentExtensions.h"
 
 namespace WebCore {
 
 PageAnimator::PageAnimator(Page* page)
     : m_page(page)
     , m_animationFramePending(false)
     , m_servicingAnimations(false)
+    , m_updatingLayoutAndStyleForPainting(false)
 {
 }
 
 void PageAnimator::serviceScriptedAnimations(double monotonicAnimationStartTime)
 {
     m_animationFramePending = false;
     TemporaryChange<bool> servicing(m_servicingAnimations, true);
 
     for (RefPtr<LocalFrame> frame = m_page->mainFrame(); frame; frame = frame->tree().traverseNext()) {
         frame->view()->serviceScrollAnimations();
         DocumentAnimations::updateAnimationTimingForAnimationFrame(*frame->document(), monotonicAnimationStartTime);
         SVGDocumentExtensions::serviceOnAnimationFrame(*frame->document(), monotonicAnimationStartTime);
     }
 
     Vector<RefPtr<Document> > documents;
     for (LocalFrame* frame = m_page->mainFrame(); frame; frame = frame->tree().traverseNext())
         documents.append(frame->document());
 
     for (size_t i = 0; i < documents.size(); ++i)
         documents[i]->serviceScriptedAnimations(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();
 }
 
 }