Drop frontbuffers with ui-use-gpu-process, synchronized with browser, decoupled from backbuffer dro…

ui/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/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 292 matching lines @@
    return test_context;
   } else {
     return ContextFactory::GetInstance()->CreateContext(this);
   }
 }
 
 void Compositor::didRebindGraphicsContext(bool success) {
 }
 
 void Compositor::didCommitAndDrawFrame() {
+  currently_compositing_ = true;
   FOR_EACH_OBSERVER(CompositorObserver,
                     observer_list_,
                     OnCompositingStarted(this));
 }
 
 void Compositor::didCompleteSwapBuffers() {
   NotifyEnd();
 }
 
 void Compositor::scheduleComposite() {
@@ skipping 17 matching lines @@
     memcpy(&pixels[row * row_size],
            &pixels[bitmap_size - (row + 1) * row_size],
            row_size);
     memcpy(&pixels[bitmap_size - (row + 1) * row_size],
            tmp_row.get(),
            row_size);
   }
 }
 
 void Compositor::NotifyEnd() {
+  currently_compositing_ = false;
   FOR_EACH_OBSERVER(CompositorObserver,
                     observer_list_,
                     OnCompositingEnded(this));
 }
 
 COMPOSITOR_EXPORT void SetupTestCompositor() {
   if (!CommandLine::ForCurrentProcess()->HasSwitch(
       switches::kDisableTestCompositor)) {
     test_compositor_enabled = true;
   }
 #if defined(OS_CHROMEOS)
   // If the test is running on the chromeos envrionment (such as
   // device or vm bots), use the real compositor.
   if (base::chromeos::IsRunningOnChromeOS())
     test_compositor_enabled = false;
 #endif
 }
 
 COMPOSITOR_EXPORT void DisableTestCompositor() {
   test_compositor_enabled = false;
 }
 
 COMPOSITOR_EXPORT bool IsTestCompositorEnabled() {
   return test_compositor_enabled;
 }
 
 }  // namespace ui