Optional <TimeDelta> since they may be non existent.

components/page_load_metrics/browser/metrics_web_contents_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 "components/page_load_metrics/browser/metrics_web_contents_observer.h"
 
 #include <vector>
 
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 266 matching lines @@
   AssertNoTimingReported();
   CheckErrorEvent(ERR_IPC_WITH_NO_RELEVANT_LOAD, 1);
   CheckTotalErrorEvents();
 }
 
 TEST_F(MetricsWebContentsObserverTest, DontLogAbortChains) {
   NavigateAndCommit(GURL(kDefaultTestUrl));
   NavigateAndCommit(GURL(kDefaultTestUrl2));
   NavigateAndCommit(GURL(kDefaultTestUrl));
   histogram_tester_.ExpectTotalCount(internal::kAbortChainSizeNewNavigation, 0);
-  CheckErrorEvent(ERR_NO_IPCS_RECEIVED, 2);
+  CheckNoErrorEvents();
   CheckTotalErrorEvents();
 }
 
 TEST_F(MetricsWebContentsObserverTest, LogAbortChains) {
   content::WebContentsTester* web_contents_tester =
       content::WebContentsTester::For(web_contents());
   content::RenderFrameHostTester* rfh_tester =
       content::RenderFrameHostTester::For(main_rfh());
   // Start and abort three loads before one finally commits.
   web_contents_tester->StartNavigation(GURL(kDefaultTestUrl));
@@ skipping 60 matching lines @@
   rfh_tester->SimulateNavigationStop();
 
   web_contents()->Stop();
 
   histogram_tester_.ExpectTotalCount(internal::kAbortChainSizeNoCommit, 1);
   histogram_tester_.ExpectBucketCount(internal::kAbortChainSizeNoCommit, 3,
                                       1);
 }
 
 }  // namespace page_load_metrics