Update the documentation for LoadCommittedDetails::previous_url.

content/public/browser/navigation_details.h

 // Copyright (c) 2012 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.
 
 #ifndef CONTENT_PUBLIC_BROWSER_NAVIGATION_DETAILS_H_
 #define CONTENT_PUBLIC_BROWSER_NAVIGATION_DETAILS_H_
 
 #include <string>
 #include "content/common/content_export.h"
 #include "content/public/browser/navigation_type.h"
@@ skipping 17 matching lines @@
 
   // The type of navigation that just occurred. Note that not all types of
   // navigations in the enum are valid here, since some of them don't actually
   // cause a "commit" and won't generate this notification.
   content::NavigationType type;
 
   // The index of the previously committed navigation entry. This will be -1
   // if there are no previous entries.
   int previous_entry_index;
 
-  // The previous URL that the user was on. This may be empty if none.
+  // The previous main frame URL that the user was on. This may be empty if
+  // there was no last committed entry.

[Avi (use Gerrit), 2015/11/09 22:42:24]

How does this interact with your change to make sure there always is a
last-committed entry? :)

[Charlie Reis, 2015/11/09 22:55:28]

Yep, it won't be possible after https://codereview.chromium.org/1309323004/.  I
hadn't updated the previous_url case yet in that CL, but I just left myself a
note to do it.  :)

   GURL previous_url;
 
   // True if the committed entry has replaced the exisiting one.
   // A non-user initiated redirect causes such replacement.
   bool did_replace_entry;
 
   // True if the navigation was in-page. This means that the active entry's
   // URL and the |previous_url| are the same except for reference fragments.
   bool is_in_page;
 
@@ skipping 34 matching lines @@
   // count items were removed from the back of the list.
   bool from_front;
 
   // Number of items removed.
   int count;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_NAVIGATION_DETAILS_H_