not for commit/review (thread cost tracker)

cc/debug/worker_thread_cost_tracker.cc

Index: cc/debug/worker_thread_cost_tracker.cc
diff --git a/cc/debug/worker_thread_cost_tracker.cc b/cc/debug/worker_thread_cost_tracker.cc
new file mode 100644
index 0000000000000000000000000000000000000000..780dc71ad631b854fc4e2fa8cab14a98cbf5bea3
--- /dev/null
+++ b/cc/debug/worker_thread_cost_tracker.cc
@@ -0,0 +1,59 @@
+// 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 "cc/debug/worker_thread_cost_tracker.h"
+
+#include "base/logging.h"
+
+namespace cc {
+
+WorkerThreadCostTracker::WorkerThreadCostTracker() : source_frame_number_(0) {
+}
+
+WorkerThreadCostTracker::~WorkerThreadCostTracker() {
+}
+
+scoped_ptr<WorkerThreadCostTracker::Probe>
+WorkerThreadCostTracker::CreateProbe() {
+  return make_scoped_ptr(new Probe(this, source_frame_number_));
+}
+
+WorkerThreadCostTracker::Probe::Probe(WorkerThreadCostTracker* tracker,
+                                      int tracked_source_frame_number)
+    : tracker_(tracker),
+      tracked_source_frame_number_(tracked_source_frame_number),
+      tracker_thread_id_(base::PlatformThread::CurrentId()),
+      started_(false) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+}
+
+WorkerThreadCostTracker::Probe::~Probe() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK(!started_);
+  if (tracker_->source_frame_number_ == tracked_source_frame_number_)
+    tracker_->add_cost(cost_);
+}
+
+void WorkerThreadCostTracker::Probe::Start(int source_frame_number) {
+  DCHECK(!started_);
+  // If this start request is for a wrong frame number, abort.
+  if (source_frame_number != tracked_source_frame_number_)
+    return;
+  // If this is being run on the same thread as the main tracker (i.e. this is
+  // not a worker thread), abort.
+  if (tracker_thread_id_ == base::PlatformThread::CurrentId())
+    return;
+
+  start_ = base::TimeTicks::HighResNow();
+  started_ = true;
+}
+
+void WorkerThreadCostTracker::Probe::Stop() {
+  if (!started_)
+    return;
+  cost_ = base::TimeTicks::HighResNow() - start_;
+  started_ = false;
+}
+
+}  // namespace cc