Guard against duplicate adds in PrerenderLinkManager.

chrome/browser/prerender/prerender_link_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_link_manager.h"
 
 #include <limits>
 #include <set>
 #include <utility>
 
@@ skipping 49 matching lines @@
     }
   }
 }
 
 void PrerenderLinkManager::OnAddPrerender(int launcher_child_id,
                                           int prerender_id,
                                           const GURL& url,
                                           const content::Referrer& referrer,
                                           const gfx::Size& size,
                                           int render_view_route_id) {
-  DCHECK_EQ(static_cast<LinkPrerender*>(NULL),
-            FindByLauncherChildIdAndPrerenderId(launcher_child_id,
-                                                prerender_id));
+  // TODO(gavinp): Determine why WebKit appears to be sending duplicate adds,
+  // and prevent it.
+  if (FindByLauncherChildIdAndPrerenderId(launcher_child_id, prerender_id))
+    return;
+
   content::RenderProcessHost* rph =
       content::RenderProcessHost::FromID(launcher_child_id);
   // Guests inside <webview> do not support cross-process navigation and so we
   // do not allow guests to prerender content.
   if (rph && rph->IsGuest())
     return;
 
   LinkPrerender
       prerender(launcher_child_id, prerender_id, url, referrer, size,
                 render_view_route_id, manager_->GetCurrentTimeTicks());
@@ skipping 261 matching lines @@
   LinkPrerender* prerender = FindByPrerenderHandle(prerender_handle);
   if (!prerender)
     return;
 
   Send(prerender->launcher_child_id,
        new PrerenderMsg_OnPrerenderAddAlias(prerender->prerender_id,
                                             alias_url));
 }
 
 }  // namespace prerender