Implement service-side surface synchronization

cc/surfaces/pending_frame_observer.h

Index: cc/surfaces/pending_frame_observer.h
diff --git a/cc/surfaces/pending_frame_observer.h b/cc/surfaces/pending_frame_observer.h
new file mode 100644
index 0000000000000000000000000000000000000000..10cec029369f294cd509afae56cba65afc23c2f2
--- /dev/null
+++ b/cc/surfaces/pending_frame_observer.h
@@ -0,0 +1,31 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.

[vmpstr, 2017/02/07 22:46:19]

nit: 2017

[Fady Samuel, 2017/02/08 00:52:49]

Done.

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CC_SURFACES_PENDING_FRAME_OBSERVER_H_
+#define CC_SURFACES_PENDING_FRAME_OBSERVER_H_
+
+#include "cc/surfaces/surface_id.h"
+
+namespace cc {
+
+using SurfaceDependencies = std::unordered_set<SurfaceId, SurfaceIdHash>;
+
+class Surface;
+
+class PendingFrameObserver {
+ public:
+  virtual void OnSurfaceActivated(Surface* surface) = 0;
+  virtual void OnSurfaceChanged(

[vmpstr, 2017/02/07 22:46:19]

Is this OnSurfaceDependenciesChanged or can surface itself change without
dependencies changing? If it's the former, I think OnSurfaceDependenciesChanged
is a better name

[Fady Samuel, 2017/02/08 00:52:49]

Done.

+      Surface* surface,
+      const SurfaceDependencies& added_dependencies,
+      const SurfaceDependencies& removed_dependencies) = 0;
+  virtual void OnSurfaceDiscarded(Surface* surface) = 0;
+
+ protected:
+  virtual ~PendingFrameObserver() {}
+};
+
+}  // namespace cc
+
+#endif  // CC_SURFACES_PENDING_FRAME_OBSERVER_H_