Add trace events in NavigationControllerImpl::back/forward(...).

content/browser/frame_host/navigation_controller_impl.cc

 // Copyright 2013 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.
 
 /*
  * Copyright (C) 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved.
  *     (http://www.torchmobile.com/)
  *
@@ skipping 568 matching lines @@
 bool NavigationControllerImpl::CanGoForward() const {
   return CanGoToOffset(1);
 }
 
 bool NavigationControllerImpl::CanGoToOffset(int offset) const {
   int index = GetIndexForOffset(offset);
   return index >= 0 && index < GetEntryCount();
 }
 
 void NavigationControllerImpl::GoBack() {
   // Call GoToIndex rather than GoToOffset to get the NOTREACHED() check.

[tdresser, 2017/03/16 12:24:38]

Move the comment below the trace event, it's referring to the GoToIndex call.
(And below)

[sunjian, 2017/03/16 18:40:30]

Acknowledged.

+  TRACE_EVENT0("browser,navigation",
+               "NavigationControllerImpl::GoBack");
   GoToIndex(GetIndexForOffset(-1));
 }
 
 void NavigationControllerImpl::GoForward() {
   // Call GoToIndex rather than GoToOffset to get the NOTREACHED() check.
+  TRACE_EVENT0("browser,navigation",
+               "NavigationControllerImpl::GoForward");
   GoToIndex(GetIndexForOffset(1));
 }
 
 void NavigationControllerImpl::GoToIndex(int index) {
   if (index < 0 || index >= static_cast<int>(entries_.size())) {
     NOTREACHED();
     return;
   }
 
   if (transient_entry_index_ != -1) {
@@ skipping 1547 matching lines @@
     }
   }
 }
 
 void NavigationControllerImpl::SetGetTimestampCallbackForTest(
     const base::Callback<base::Time()>& get_timestamp_callback) {
   get_timestamp_callback_ = get_timestamp_callback;
 }
 
 }  // namespace content