Use swap-promise to improve first* paint times

cc/output/report_time_swap_promise.h

+// 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.
+
+#ifndef CC_OUTPUT_REPORT_TIME_SWAP_PROMISE_H_
+#define CC_OUTPUT_REPORT_TIME_SWAP_PROMISE_H_
+
+#include "base/callback.h"
+#include "cc/output/swap_promise.h"
+
+namespace base {
+class SingleThreadTaskRunner;
+}
+
+namespace cc {
+
+using ReportTimeCallback = base::Callback<void(bool, double)>;
+
+class CC_EXPORT ReportTimeSwapPromise : public SwapPromise {
+ public:
+  ReportTimeSwapPromise(
+      ReportTimeCallback callback,
+      const scoped_refptr<base::SingleThreadTaskRunner>& task_runner);
+  ~ReportTimeSwapPromise() override;
+
+  void DidActivate() override {}
+  void WillSwap(CompositorFrameMetadata* metadata) override {}
+  void DidSwap() override;
+  DidNotSwapAction DidNotSwap(DidNotSwapReason reason) override;
+
+  int64_t TraceId() const override;
+
+ private:
+  ReportTimeCallback callback_;
+  scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
+};
+
+}  // namespace cc
+
+#endif  // CC_OUTPUT_REPORT_TIME_SWAP_PROMISE_H_