Replace PruneAllButActive with PruneAllButVisible.

chrome/browser/prerender/prerender_manager.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/prerender/prerender_manager.h"
 
 #include <algorithm>
 #include <functional>
 #include <string>
 #include <vector>
@@ skipping 403 matching lines @@
   if (!prerender_data)
     return false;
   DCHECK(prerender_data->contents());
   if (IsNoSwapInExperiment(prerender_data->contents()->experiment_id()))
     return false;
 
   if (WebContents* new_web_contents =
       prerender_data->contents()->prerender_contents()) {
     if (web_contents == new_web_contents)
       return false;  // Do not swap in to ourself.
+
+    // We cannot swap in if there is no last committed entry, because we would
+    // show a blank page under an existing entry from the current tab.  Even if
+    // there is a pending entry, it may not commit.
+    // TODO(creis): If there is a pending navigation and no last committed
+    // entry, we might be able to transfer the network request instead.
+    if (!new_web_contents->GetController().CanPruneAllButVisible())
+      return false;
   }
 
   // Do not use the prerendered version if there is an opener object.
   if (web_contents->HasOpener()) {
     prerender_data->contents()->Destroy(FINAL_STATUS_WINDOW_OPENER);
     return false;
   }
 
   // If we are just in the control group (which can be detected by noticing
   // that prerendering hasn't even started yet), record that |web_contents| now
@@ skipping 1085 matching lines @@
     logged_in_state_->erase(domain_key);
 }
 
 void PrerenderManager::LoggedInPredictorDataReceived(
     scoped_ptr<LoggedInStateMap> new_map) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   logged_in_state_.swap(new_map);
 }
 
 }  // namespace prerender