Add ExternalPrerenderRequestHandler and related API

chrome/browser/prerender/prerender_manager.h

Index: chrome/browser/prerender/prerender_manager.h
diff --git a/chrome/browser/prerender/prerender_manager.h b/chrome/browser/prerender/prerender_manager.h
index c8e7f642be4ec3cf0d655283de5bbe0079453cb4..920621d9b2b22fe090027b80f6973c6320f3d84c 100644
--- a/chrome/browser/prerender/prerender_manager.h
+++ b/chrome/browser/prerender/prerender_manager.h
@@ -151,6 +151,12 @@ class PrerenderManager : public base::SupportsWeakPtr<PrerenderManager>,
       content::SessionStorageNamespace* session_storage_namespace,
       const gfx::Size& size);
 
+  PrerenderHandle* AddPrerenderFromExternalRequest(
+      const GURL& url,
+      const content::Referrer& referrer,
+      content::SessionStorageNamespace* session_storage_namespace,
+      const gfx::Size& size);
+
   // If |process_id| and |view_id| refer to a running prerender, destroy
   // it with |final_status|.
   virtual void DestroyPrerenderForRenderView(int process_id,
@@ -215,6 +221,10 @@ class PrerenderManager : public base::SupportsWeakPtr<PrerenderManager>,
   bool IsWebContentsPrerendering(const content::WebContents* web_contents,
                                  Origin* origin) const;
 
+  // Whether the PrerenderManager has an active prerender with the given url and
+  // SessionStorageNamespace associated with the given WebContens.
+  bool HasPrerenderedUrl(GURL url, content::WebContents* web_contents) const;
+
   // Returns the PrerenderContents object for the given web_contents if it's
   // used for an active prerender page, otherwise returns NULL.
   PrerenderContents* GetPrerenderContents(