Remove prerender sessionStorage namespace merging (1/2)

chrome/browser/ui/browser_navigator.cc

 // 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.
 
 #include "chrome/browser/ui/browser_navigator.h"
 
 #include <algorithm>
 
 #include "base/command_line.h"
 #include "base/prefs/pref_service.h"
@@ skipping 603 matching lines @@
       params->target_contents = CreateTargetContents(*params, params->url);
 
       // This function takes ownership of |params->target_contents| until it
       // is added to a TabStripModel.
       target_contents_owner.TakeOwnership();
     } else {
       // ... otherwise if we're loading in the current tab, the target is the
       // same as the source.
       DCHECK(params->source_contents);
       params->target_contents = params->source_contents;
+
+      // Prerender can only swap in CURRENT_TAB navigations; others have
+      // different sessionStorage namespaces.
+      swapped_in_prerender = SwapInPrerender(params->url, params);

[mmenke, 2014/12/12 16:04:48]

Before the merge stuff, didn't we used to cancel on session storage mismatch, as
the prerender was probably intended for the navigation we can't use it for?  Or
am I misremembering?

[davidben, 2014/12/12 20:41:19]

Looks like we stopped doing it in
https://chromiumcodereview.appspot.com/10553029. It now just figures into the
lookup, which is probably better? I think one WC's prerenders shouldn't interact
with another's if possible.

     }
 
-    // Note: at this point, if |params->disposition| is not CURRENT_TAB,
-    // |params->target_contents| has not been attached to a Browser yet. (That
-    // happens later in this function.) However, in that case, the
-    // sessionStorage namespace could not match, so prerender will use the
-    // asynchronous codepath and still swap.
-    DCHECK(params->target_contents);
-    swapped_in_prerender = SwapInPrerender(params->url, params);
-
     if (user_initiated)
       params->target_contents->UserGestureDone();
 
     if (!swapped_in_prerender) {
       // Try to handle non-navigational URLs that popup dialogs and such, these
       // should not actually navigate.
       if (!HandleNonNavigationAboutURL(params->url)) {
         // Perform the actual navigation, tracking whether it came from the
         // renderer.
 
@@ skipping 125 matching lines @@
   bool reverse_on_redirect = false;
   content::BrowserURLHandler::GetInstance()->RewriteURLIfNecessary(
       &rewritten_url, browser_context, &reverse_on_redirect);
 
   // Some URLs are mapped to uber subpages. Do not allow them in incognito.
   return !(rewritten_url.scheme() == content::kChromeUIScheme &&
            rewritten_url.host() == chrome::kChromeUIUberHost);
 }
 
 }  // namespace chrome