Use swap-promise to improve first* paint times

cc/output/report_time_swap_promise.cc

+// 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/output/report_time_swap_promise.h"
+#include "base/bind.h"
+#include "base/single_thread_task_runner.h"
+
+namespace cc {
+
+namespace {
+double MonotonicallyIncreasingTime() {
+  return base::TimeTicks::Now().ToInternalValue() /
+         static_cast<double>(base::Time::kMicrosecondsPerSecond);
+}
+}
+
+ReportTimeSwapPromise::ReportTimeSwapPromise(
+    ReportTimeCallback callback,
+    const scoped_refptr<base::SingleThreadTaskRunner>& task_runner)
+    : callback_(callback), task_runner_(task_runner) {}
+
+ReportTimeSwapPromise::~ReportTimeSwapPromise() {}
+
+void ReportTimeSwapPromise::DidSwap() {
+  task_runner_->PostTask(
+      FROM_HERE,
+      base::BindOnce(callback_, true, MonotonicallyIncreasingTime()));
+}
+
+SwapPromise::DidNotSwapAction ReportTimeSwapPromise::DidNotSwap(
+    SwapPromise::DidNotSwapReason reason) {
+  task_runner_->PostTask(FROM_HERE, base::BindOnce(callback_, false, 0));
+  return SwapPromise::DidNotSwapAction::BREAK_PROMISE;
+}
+
+int64_t ReportTimeSwapPromise::TraceId() const {
+  return 0;
+}
+
+}  // namespace cc