SurfaceDependencyTracker: Only observe BeginFrames if a deadline is needed

cc/surfaces/surface_dependency_tracker.h

Index: cc/surfaces/surface_dependency_tracker.h
diff --git a/cc/surfaces/surface_dependency_tracker.h b/cc/surfaces/surface_dependency_tracker.h
index f5bab833737be63610950307b0ea4d55125fc76f..45b543cd6fe2bf2970df025d20d1740ec59c00dd 100644
--- a/cc/surfaces/surface_dependency_tracker.h
+++ b/cc/surfaces/surface_dependency_tracker.h
@@ -5,12 +5,13 @@
 #ifndef CC_SURFACES_SURFACE_DEPENDENCY_TRACKER_H_
 #define CC_SURFACES_SURFACE_DEPENDENCY_TRACKER_H_
 
-#include "cc/scheduler/begin_frame_source.h"
 #include "cc/surfaces/surface.h"
+#include "cc/surfaces/surface_dependency_deadline.h"
 #include "cc/surfaces/surfaces_export.h"
 
 namespace cc {
 
+class BeginFrameSource;
 class SurfaceManager;
 
 // SurfaceDependencyTracker tracks unresolved dependencies blocking
@@ -28,17 +29,19 @@ class SurfaceManager;
 // TODO(fsamuel): Deadlines should not be global. They should be scoped to a
 // surface subtree. However, that will not be possible until SurfaceReference
 // work is complete.
-class CC_SURFACES_EXPORT SurfaceDependencyTracker : public BeginFrameObserver {
+class CC_SURFACES_EXPORT SurfaceDependencyTracker {
  public:
   SurfaceDependencyTracker(SurfaceManager* surface_manager,
                            BeginFrameSource* begin_frame_source);
-  ~SurfaceDependencyTracker() override;
+  ~SurfaceDependencyTracker();
 
   // Called when |surface| has a pending CompositorFrame and it wishes to be
   // informed when that surface's dependencies are resolved.
   void RequestSurfaceResolution(Surface* surface);
 
-  bool has_deadline() const { return frames_since_deadline_set_.has_value(); }
+  bool has_deadline() const { return deadline_.has_deadline(); }
+
+  void OnDeadline();
 
   void OnSurfaceActivated(Surface* surface);
   void OnSurfaceDependenciesChanged(
@@ -47,11 +50,6 @@ class CC_SURFACES_EXPORT SurfaceDependencyTracker : public BeginFrameObserver {
       const base::flat_set<SurfaceId>& removed_dependencies);
   void OnSurfaceDiscarded(Surface* surface);
 
-  // BeginFrameObserver implementation.
-  void OnBeginFrame(const BeginFrameArgs& args) override;
-  const BeginFrameArgs& LastUsedBeginFrameArgs() const override;
-  void OnBeginFrameSourcePausedChanged(bool paused) override;
-
  private:
   // Informs all Surfaces with pending frames blocked on the provided
   // |surface_id| that there is now an active frame available in Surface
@@ -60,15 +58,9 @@ class CC_SURFACES_EXPORT SurfaceDependencyTracker : public BeginFrameObserver {
 
   SurfaceManager* const surface_manager_;
 
-  // The last begin frame args generated by the begin frame source.
-  BeginFrameArgs last_begin_frame_args_;
-
-  // The BeginFrameSource used to set deadlines.
-  BeginFrameSource* const begin_frame_source_;
-
-  // The number of BeginFrames observed since a deadline was set. If
-  // base::nullopt_t then a deadline is not set.
-  base::Optional<uint32_t> frames_since_deadline_set_;
+  // This object tracks the deadline when all pending CompositorFrames in the
+  // system will be activated.
+  SurfaceDependencyDeadline deadline_;
 
   // A map from a SurfaceId to the set of Surfaces blocked on that SurfaceId.
   std::unordered_map<SurfaceId, base::flat_set<SurfaceId>, SurfaceIdHash>