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

chrome/browser/android/offline_pages/prerender_adapter.cc

 // 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.
 
 #include "chrome/browser/android/offline_pages/prerender_adapter.h"
 
 #include "chrome/browser/prerender/prerender_manager.h"
 #include "chrome/browser/prerender/prerender_manager_factory.h"
 #include "content/public/browser/browser_context.h"
 #include "content/public/browser/web_contents.h"
 #include "ui/gfx/geometry/size.h"
 
 namespace offline_pages {
 
 PrerenderAdapter::Observer::Observer() {}
 PrerenderAdapter::Observer::~Observer() {}
 
 PrerenderAdapter::PrerenderAdapter(PrerenderAdapter::Observer* observer)
     : observer_(observer) {
   DCHECK(observer);
 }
 
 PrerenderAdapter::~PrerenderAdapter() {
   if (IsActive())
     DestroyActive();
 }
 
-bool PrerenderAdapter::CanPrerender() const {
-  return prerender::PrerenderManager::IsPrerenderingPossible();
-}
-
 bool PrerenderAdapter::StartPrerender(
     content::BrowserContext* browser_context,
     const GURL& url,
     content::SessionStorageNamespace* session_storage_namespace,
     const gfx::Size& size) {
   DCHECK(!IsActive());
-  DCHECK(CanPrerender());
 
   prerender::PrerenderManager* manager =
       prerender::PrerenderManagerFactory::GetForBrowserContext(browser_context);
   DCHECK(manager);
 
   // AddPrerenderForOffline() triggers the start event, and it is before the
   // observer is set.
   active_handle_ =
       manager->AddPrerenderForOffline(url, session_storage_namespace, size);
   if (!active_handle_)
@@ skipping 52 matching lines @@
 }
 
 void PrerenderAdapter::OnPrerenderStop(prerender::PrerenderHandle* handle) {
   if (IsActive()) {
     DCHECK_EQ(active_handle_.get(), handle);
     observer_->OnPrerenderStop();
   }
 }
 
 }  // namespace offline_pages