Buffer cross frame paint timing updates.

chrome/common/page_load_metrics/test/weak_mock_timer.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 "chrome/common/page_load_metrics/test/weak_mock_timer.h"
+
+namespace page_load_metrics {
+namespace test {
+
+WeakMockTimer::WeakMockTimer()
+    : MockTimer(false /* retain_user_task */, false /* is_repeating */) {}
+
+WeakMockTimerProvider::WeakMockTimerProvider() {}
+WeakMockTimerProvider::~WeakMockTimerProvider() {}
+
+base::MockTimer* WeakMockTimerProvider::GetMockTimer() const {
+  return timer_.get();
+}
+
+void WeakMockTimerProvider::SetMockTimer(base::WeakPtr<WeakMockTimer> timer) {
+  timer_ = timer;
+}
+
+}  // namespace test
+}  // namespace page_load_metrics