RenderWidget's scheduleComposite should return a bool. (true iff a prompt composite will come).

ui/gfx/compositor/compositor.cc

 // Copyright (c) 2012 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 "ui/gfx/compositor/compositor.h"
 
 #include "base/command_line.h"
 #include "base/threading/thread_restrictions.h"
 #include "third_party/WebKit/Source/WebKit/chromium/public/WebCompositor.h"
 #include "third_party/WebKit/Source/WebKit/chromium/public/platform/WebFloatPoint.h"
@@ skipping 285 matching lines @@
 void Compositor::didCommitAndDrawFrame() {
   FOR_EACH_OBSERVER(CompositorObserver,
                     observer_list_,
                     OnCompositingStarted(this));
 }
 
 void Compositor::didCompleteSwapBuffers() {
   NotifyEnd();
 }
 
-void Compositor::scheduleComposite() {
+#if defined(WEBLAYERTREEVIEWCLIENT_SCHEDULECOMPOSITE_RETURNS_BOOL)
+#define SCHEDULECOMPOSITE_RETURN_TYPE bool
+#else
+#define SCHEDULECOMPOSITE_RETURN_TYPE void
+#endif
+
+SCHEDULECOMPOSITE_RETURN_TYPE Compositor::scheduleComposite() {
   ScheduleDraw();
+#if defined(WEBLAYERTREEVIEWCLIENT_SCHEDULECOMPOSITE_RETURNS_BOOL)
+  return true;
+#endif
 }
 
 void Compositor::SwizzleRGBAToBGRAAndFlip(unsigned char* pixels,
                                           const gfx::Size& image_size) {
   // Swizzle from RGBA to BGRA
   size_t bitmap_size = 4 * image_size.width() * image_size.height();
   for(size_t i = 0; i < bitmap_size; i += 4)
     std::swap(pixels[i], pixels[i + 2]);
 
   // Vertical flip to transform from GL co-ords
@@ skipping 27 matching lines @@
 
 COMPOSITOR_EXPORT void DisableTestCompositor() {
   test_compositor_enabled = false;
 }
 
 COMPOSITOR_EXPORT bool IsTestCompositorEnabled() {
   return test_compositor_enabled;
 }
 
 }  // namespace ui