[exo] Clean up BeginFrame distribution & add acks in Surface.

components/exo/surface.h

Index: components/exo/surface.h
diff --git a/components/exo/surface.h b/components/exo/surface.h
index ecda81291a8948dcba8a9c4350a51148071d0e3e..8e4a6ad9b5635b0906474e6f367b71a8cb3dad34 100644
--- a/components/exo/surface.h
+++ b/components/exo/surface.h
@@ -15,6 +15,7 @@
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
 #include "base/observer_list.h"
+#include "cc/output/begin_frame_args.h"
 #include "cc/resources/transferable_resource.h"
 #include "cc/scheduler/begin_frame_source.h"
 #include "cc/surfaces/local_surface_id_allocator.h"
@@ -62,7 +63,8 @@ using CursorProvider = Pointer;
 class Surface : public ui::ContextFactoryObserver,
                 public aura::WindowObserver,
                 public ui::PropertyHandler,
-                public ui::CompositorVSyncManager::Observer {
+                public ui::CompositorVSyncManager::Observer,
+                public cc::BeginFrameObserverBase {
  public:
   using PropertyDeallocator = void (*)(int64_t value);
 
@@ -192,12 +194,8 @@ class Surface : public ui::ContextFactoryObserver,
   // Call this to indicate that surface is being scheduled for a draw.
   void WillDraw();
 
-  // Returns true when there's an active frame callback that requires a
-  // BeginFrame() call.
-  bool NeedsBeginFrame() const;
-
-  // Call this to indicate that it's a good time to start producing a new frame.
-  void BeginFrame(base::TimeTicks frame_time);
+  // Called when the begin frame source has changed.
+  void SetBeginFrameSource(cc::BeginFrameSource* begin_frame_source);
 
   // Check whether this Surface and its children need to create new cc::Surface
   // IDs for their contents next time they get new buffer contents.
@@ -222,6 +220,10 @@ class Surface : public ui::ContextFactoryObserver,
     return pending_damage_.contains(gfx::RectToSkIRect(damage));
   }
 
+  // Overridden from cc::BeginFrameObserverBase:
+  bool OnBeginFrameDerivedImpl(const cc::BeginFrameArgs& args) override;
+  void OnBeginFrameSourcePausedChanged(bool paused) override {}
+
  private:
   struct State {
     State();
@@ -282,6 +284,9 @@ class Surface : public ui::ContextFactoryObserver,
   // current_resource_.
   void UpdateSurface(bool full_damage);
 
+  // Adds/Removes begin frame observer based on state.
+  void UpdateNeedsBeginFrame();
+
   // This returns true when the surface has some contents assigned to it.
   bool has_contents() const { return !!current_buffer_.buffer(); }
 
@@ -389,6 +394,11 @@ class Surface : public ui::ContextFactoryObserver,
   // references to surfaces.
   scoped_refptr<cc::SurfaceReferenceFactory> surface_reference_factory_;
 
+  // The begin frame source being observed.
+  cc::BeginFrameSource* begin_frame_source_ = nullptr;
+  bool needs_begin_frame_ = false;
+  cc::BeginFrameAck current_begin_frame_ack_;
+
   DISALLOW_COPY_AND_ASSIGN(Surface);
 };