SurfaceDependencyTracker: Only observe BeginFrames if a deadline is needed

cc/surfaces/surface_dependency_deadline.cc

Index: cc/surfaces/surface_dependency_deadline.cc
diff --git a/cc/surfaces/surface_dependency_deadline.cc b/cc/surfaces/surface_dependency_deadline.cc
new file mode 100644
index 0000000000000000000000000000000000000000..7bdbefcc5469a4c725e04e88d589e3ed32a58a9c
--- /dev/null
+++ b/cc/surfaces/surface_dependency_deadline.cc
@@ -0,0 +1,55 @@
+// Copyright 2017 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 "cc/surfaces/surface_dependency_deadline.h"
+
+#include "cc/surfaces/surface_dependency_tracker.h"
+
+namespace cc {
+
+SurfaceDependencyDeadline::SurfaceDependencyDeadline(
+    SurfaceDependencyTracker* dependency_tracker,
+    BeginFrameSource* begin_frame_source)
+    : dependency_tracker_(dependency_tracker),
+      begin_frame_source_(begin_frame_source) {
+  DCHECK(begin_frame_source_);
+}
+
+SurfaceDependencyDeadline::~SurfaceDependencyDeadline() {
+  // The deadline must be canceled before destruction.
+  DCHECK(!number_of_frames_to_deadline_);
+}
+
+void SurfaceDependencyDeadline::Set(uint32_t number_of_frames_to_deadline) {
+  DCHECK_GT(number_of_frames_to_deadline, 0u);
+  DCHECK(!number_of_frames_to_deadline_);
+  number_of_frames_to_deadline_ = number_of_frames_to_deadline;
+  begin_frame_source_->AddObserver(this);
+}
+
+void SurfaceDependencyDeadline::Cancel() {
+  if (!number_of_frames_to_deadline_)
+    return;
+  begin_frame_source_->RemoveObserver(this);
+  number_of_frames_to_deadline_.reset();
+}
+
+// BeginFrameObserver implementation.
+void SurfaceDependencyDeadline::OnBeginFrame(const BeginFrameArgs& args) {
+  last_begin_frame_args_ = args;
+  if (--(*number_of_frames_to_deadline_) > 0)
+    return;
+
+  Cancel();
+  dependency_tracker_->OnDeadline();
+}
+
+const BeginFrameArgs& SurfaceDependencyDeadline::LastUsedBeginFrameArgs()
+    const {
+  return last_begin_frame_args_;
+}
+
+void SurfaceDependencyDeadline::OnBeginFrameSourcePausedChanged(bool paused) {}
+
+}  // namespace cc