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

ui/compositor/compositor.cc

Index: ui/compositor/compositor.cc
diff --git a/ui/compositor/compositor.cc b/ui/compositor/compositor.cc
index 9ad531afc40668b06356b4356d9a413134ab6893..2fd83f928b94994f88189940cc5822632fb8f75a 100644
--- a/ui/compositor/compositor.cc
+++ b/ui/compositor/compositor.cc
@@ -310,6 +310,7 @@ void Compositor::didRebindGraphicsContext(bool success) {
 }
 
 void Compositor::didCommitAndDrawFrame() {
+  currently_compositing_ = true;
   FOR_EACH_OBSERVER(CompositorObserver,
                     observer_list_,
                     OnCompositingStarted(this));
@@ -347,6 +348,7 @@ void Compositor::SwizzleRGBAToBGRAAndFlip(unsigned char* pixels,
 }
 
 void Compositor::NotifyEnd() {
+  currently_compositing_ = false;
   FOR_EACH_OBSERVER(CompositorObserver,
                     observer_list_,
                     OnCompositingEnded(this));