[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(

[dewittj, 2016/09/13 17:03:17]

nit: I have a slight preference for putting it into a local unique_ptr instead,
and update session_contents_ after we know it'll be used.

[dougarnett, 2016/09/13 18:15:22]

Done. Please check.

       content::WebContents::CreateParams(browser_context_)));
   content::SessionStorageNamespace* sessionStorageNamespace =
       session_contents_->GetController().GetDefaultSessionStorageNamespace();
   gfx::Size renderWindowSize = session_contents_->GetContainerBounds().size();
   bool accepted = adapter_->StartPrerender(
       browser_context_, url, sessionStorageNamespace, renderWindowSize);
-  if (!accepted)
+  if (!accepted) {
+    session_contents_.reset(nullptr);

[dewittj, 2016/09/13 17:03:17]

It is unfortunate that we have to create a web contents only to destroy it
immediately afterwards.  I suppose there's no way to do this without it?

[dougarnett, 2016/09/13 18:15:22]

Acknowledged.

     return false;
+  }
 
   DCHECK(adapter_->IsActive());
   snapshot_controller_.reset(
       new SnapshotController(base::ThreadTaskRunnerHandle::Get(), this));
   callback_ = callback;
   state_ = State::PENDING;
   return true;
 }
 
 void PrerenderingLoader::StopLoading() {
@@ skipping 133 matching lines @@
 void PrerenderingLoader::CancelPrerender() {
   if (adapter_->IsActive()) {
     adapter_->DestroyActive();
   }
   snapshot_controller_.reset(nullptr);
   session_contents_.reset(nullptr);
   state_ = State::IDLE;
 }
 
 }  // namespace offline_pages