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

chrome/browser/android/offline_pages/prerendering_loader.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_PRERENDERING_LOADER_H_
 #define CHROME_BROWSER_ANDROID_OFFLINE_PAGES_PRERENDERING_LOADER_H_
 
 #include <memory>
 
 #include "base/callback.h"
@@ skipping 35 matching lines @@
   virtual bool LoadPage(const GURL& url, const LoadPageCallback& callback);
 
   // Stops (completes or cancels) the load request. Must be called when
   // LoadPageCallback is done with consuming the contents. May be called
   // prior to LoadPageCallback in order to cancel the current request (in
   // which case the callback will not be run).
   // This loader should also be responsible for stopping offline
   // prerenders when Chrome is transitioned to foreground.
   virtual void StopLoading();
 
-  // Returns whether prerendering is possible for this device's configuration
-  // and the browser context.
-  virtual bool CanPrerender();
-
   // Returns whether the loader is idle and able to accept new LoadPage
   // request.
   virtual bool IsIdle();
 
   // Returns whether the loader has successfully loaded web contents.
   // Note that |StopLoading()| should be used to clear this state once
   // the loaded web contents are no longer needed.
   virtual bool IsLoaded();
 
   // Overrides the prerender stack adapter for unit testing.
@@ skipping 49 matching lines @@
   // Callback to call when the active load request completes, fails, or is
   // canceled.
   LoadPageCallback callback_;
 
   DISALLOW_COPY_AND_ASSIGN(PrerenderingLoader);
 };
 
 }  // namespace offline_pages
 
 #endif  // CHROME_BROWSER_ANDROID_OFFLINE_PAGES_PRERENDERING_LOADER_H_