Replace PruneAllButActive with PruneAllButVisible.

chrome/browser/ui/browser_instant_controller.cc

 // Copyright 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_instant_controller.h"
 
 #include "base/bind.h"
 #include "base/prefs/pref_service.h"
 #include "chrome/browser/extensions/extension_service.h"
 #include "chrome/browser/extensions/extension_web_ui.h"
@@ skipping 76 matching lines @@
     content::WebContents** target_contents) {
   if (url != GURL(chrome::kChromeUINewTabURL))
     return false;
 
   GURL extension_url(url);
   if (ExtensionWebUI::HandleChromeURLOverride(&extension_url, profile())) {
     // If there is an extension overriding the NTP do not use the Instant NTP.
     return false;
   }
 
+  // Make sure the instant WebContents is in a valid state (i.e., has a last
+  // committed entry, no transient entry, and no existing pending entry).
   scoped_ptr<content::WebContents> instant_ntp = instant_.ReleaseNTPContents();
-  if (!instant_ntp)
+  if (!instant_ntp || !instant_ntp->GetController().CanPruneAllButVisible())
     return false;
 
   *target_contents = instant_ntp.get();
   if (source_contents) {
-    instant_ntp->GetController().CopyStateFromAndPrune(
-        &source_contents->GetController());
+    CHECK(instant_ntp->GetController().CopyStateFromAndPrune(
+              &source_contents->GetController()));
     ReplaceWebContentsAt(
         browser_->tab_strip_model()->GetIndexOfWebContents(source_contents),
         instant_ntp.Pass());
   } else {
-    instant_ntp->GetController().PruneAllButActive();
+    CHECK(instant_ntp->GetController().PruneAllButVisible());
     // If |source_contents| is NULL, then the caller is responsible for
     // inserting instant_ntp into the tabstrip and will take ownership.
     ignore_result(instant_ntp.release());
   }
   return true;
 }
 
 bool BrowserInstantController::OpenInstant(WindowOpenDisposition disposition) {
   // Unsupported dispositions.
   if (disposition == NEW_BACKGROUND_TAB || disposition == NEW_WINDOW)
@@ skipping 276 matching lines @@
     if (!instant_service->IsInstantProcess(
             contents->GetRenderProcessHost()->GetID()))
       continue;
 
     // Reload the contents to ensure that it gets assigned to a non-priviledged
     // renderer.
     contents->GetController().Reload(false);
   }
   instant_.OnDefaultSearchProviderChanged();
 }