[OfflinePages] Improve visiblity/handling of "Loading not started" case

chrome/browser/android/offline_pages/prerender_adapter.h

 // Copyright 2016 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.
 
 #ifndef CHROME_BROWSER_ANDROID_OFFLINE_PAGES_PRERENDER_ADAPTER_H_
 #define CHROME_BROWSER_ANDROID_OFFLINE_PAGES_PRERENDER_ADAPTER_H_
 
 #include <memory>
 
 #include "chrome/browser/prerender/prerender_handle.h"
@@ skipping 30 matching lines @@
     virtual void OnPrerenderStop() = 0;
 
    protected:
     Observer();
     virtual ~Observer();
   };
 
   explicit PrerenderAdapter(PrerenderAdapter::Observer* observer);
   ~PrerenderAdapter() override;
 
-  // Returns whether prerendering is enabled and configured.
-  virtual bool CanPrerender() const;
-
   // Starts prerendering |url| for offlining. There must be no active
   // prerender request when calling this. Returns whether it was able
   // to start the prerendering operation.
   virtual bool StartPrerender(
       content::BrowserContext* browser_context,
       const GURL& url,
       content::SessionStorageNamespace* session_storage_namespace,
       const gfx::Size& size);
 
   // Returns a pointer to the prerendered WebContents. This should only be
@@ skipping 30 matching lines @@
 
   // Observer of active handle events. Not owned.
   PrerenderAdapter::Observer* observer_;
 
   DISALLOW_COPY_AND_ASSIGN(PrerenderAdapter);
 };
 
 }  // namespace offline_pages
 
 #endif  // CHROME_BROWSER_ANDROID_OFFLINE_PAGES_PRERENDER_ADAPTER_H_