[Offline Pages] Fixes PrerenderingLoader bug to clear session_contents_ when PrerenderManager does …

chrome/browser/android/offline_pages/prerendering_loader.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/prerendering_loader.h"
 
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/threading/thread_task_runner_handle.h"
@@ skipping 24 matching lines @@
     DVLOG(1)
         << "WARNING: Existing request in progress or waiting for StopLoading()";
     return false;
   }
   if (!CanPrerender())
     return false;
 
   // Create a WebContents instance to define and hold a SessionStorageNamespace
   // for this load request.
   DCHECK(!session_contents_.get());
-  session_contents_.reset(content::WebContents::Create(
-      content::WebContents::CreateParams(browser_context_)));
+  std::unique_ptr<content::WebContents> new_web_contents(
+      content::WebContents::Create(
+          content::WebContents::CreateParams(browser_context_)));
   content::SessionStorageNamespace* sessionStorageNamespace =
-      session_contents_->GetController().GetDefaultSessionStorageNamespace();
-  gfx::Size renderWindowSize = session_contents_->GetContainerBounds().size();
+      new_web_contents->GetController().GetDefaultSessionStorageNamespace();
+  gfx::Size renderWindowSize = new_web_contents->GetContainerBounds().size();
   bool accepted = adapter_->StartPrerender(
       browser_context_, url, sessionStorageNamespace, renderWindowSize);
   if (!accepted)
     return false;
 
   DCHECK(adapter_->IsActive());
   snapshot_controller_.reset(
       new SnapshotController(base::ThreadTaskRunnerHandle::Get(), this));
   callback_ = callback;
+  session_contents_.swap(new_web_contents);
   state_ = State::PENDING;
   return true;
 }
 
 void PrerenderingLoader::StopLoading() {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
   CancelPrerender();
 }
 
 bool PrerenderingLoader::CanPrerender() {
@@ skipping 128 matching lines @@
 void PrerenderingLoader::CancelPrerender() {
   if (adapter_->IsActive()) {
     adapter_->DestroyActive();
   }
   snapshot_controller_.reset(nullptr);
   session_contents_.reset(nullptr);
   state_ = State::IDLE;
 }
 
 }  // namespace offline_pages