Ozone: Avoid blocking in Swapbuffer Call.

ui/ozone/platform/dri/gbm_surfaceless.cc

 // 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 "ui/ozone/platform/dri/gbm_surfaceless.h"
 
 #include "ui/ozone/platform/dri/dri_vsync_provider.h"
 #include "ui/ozone/platform/dri/dri_window_delegate.h"
 #include "ui/ozone/platform/dri/gbm_buffer.h"
 #include "ui/ozone/platform/dri/hardware_display_controller.h"
+#include "ui/ozone/platform/dri/page_flip_event_handler.h"
 
 namespace ui {
 
-GbmSurfaceless::GbmSurfaceless(DriWindowDelegate* window_delegate)
-    : window_delegate_(window_delegate) {
+GbmSurfaceless::GbmSurfaceless(DriWindowDelegate* window_delegate,
+                               PageFlipEventHandler* handler)
+    : window_delegate_(window_delegate), flip_handler_(handler) {
 }
 
 GbmSurfaceless::~GbmSurfaceless() {}
 
 intptr_t GbmSurfaceless::GetNativeWindow() {
   NOTREACHED();
   return 0;
 }
 
 bool GbmSurfaceless::ResizeNativeWindow(const gfx::Size& viewport_size) {
   NOTIMPLEMENTED();
   return false;
 }
 
 bool GbmSurfaceless::OnSwapBuffers() {
   HardwareDisplayController* controller = window_delegate_->GetController();
   if (!controller)
     return true;
 
   bool success = controller->SchedulePageFlip();
-  controller->WaitForPageFlipEvent();
+
+  if (flip_handler_)
+    flip_handler_->GetPageFlipCompleted(controller, callback_);
+  else
+    controller->WaitForPageFlipEvent();
 
   return success;
 }
 
 scoped_ptr<gfx::VSyncProvider> GbmSurfaceless::CreateVSyncProvider() {
   return scoped_ptr<gfx::VSyncProvider>(new DriVSyncProvider(window_delegate_));
 }
 
+void GbmSurfaceless::SetPageFlipCompletionCallback(
+    const PageFlipCompletionCallback& callback) {
+  callback_ = callback;
+}
+
 }  // namespace ui