Add support for tracking loading behavior of child frames.

chrome/renderer/page_load_metrics/metrics_render_frame_observer_unittest.cc

 // Copyright (c) 2015 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/renderer/page_load_metrics/metrics_render_frame_observer.h"
 
 #include <memory>
 #include <utility>
 
 #include "base/memory/ptr_util.h"
@@ skipping 39 matching lines @@
                ? PageLoadTiming()
                : fake_timing_ipc_sender_.expected_timings().back();
   }
 
   void VerifyExpectedTimings() const {
     fake_timing_ipc_sender_.VerifyExpectedTimings();
   }
 
   bool ShouldSendMetrics() const override { return true; }
   bool HasNoRenderFrame() const override { return false; }
+  bool IsMainFrame() const override { return true; }
 
  private:
   FakePageTimingMetricsIPCSender fake_timing_ipc_sender_;
   mutable std::unique_ptr<base::Timer> mock_timer_;
 };
 
 typedef testing::Test MetricsRenderFrameObserverTest;
 
 TEST_F(MetricsRenderFrameObserverTest, NoMetrics) {
   TestMetricsRenderFrameObserver observer;
@@ skipping 116 matching lines @@
   timing_2.first_layout = first_layout_2;
   timing_2.dom_content_loaded_event_start = dom_event_2;
   timing_2.load_event_start = load_event_2;
   observer.ExpectPageLoadTiming(timing_2);
 
   observer.DidChangePerformanceTiming();
   mock_timer2->Fire();
 }
 
 }  // namespace page_load_metrics