Code: PepperMediaDeviceManager* PepperPlatformAudioInput::GetMediaDeviceManager() {
  DCHECK(main_message_loop_proxy_->BelongsToCurrentThread());

   RenderFrameImpl* const render_frame =
       RenderFrameImpl::FromRoutingID(render_frame_id_);
   return render_frame ?
      PepperMediaDeviceManager::GetForRenderFrame(render_frame) : NULL;
 }

Vulnerability Type: DoS 
CWE ID: CWE-399
Summary: Use-after-free vulnerability in the Pepper plugins in Google Chrome before 39.0.2171.65 allows remote attackers to cause a denial of service or possibly have unspecified other impact via crafted Flash content that triggers an attempted PepperMediaDeviceManager access outside of the object's lifetime.
Commit Message: Pepper: Access PepperMediaDeviceManager through a WeakPtr

Its lifetime is scoped to the RenderFrame, and it might go away before the
hosts that refer to it.

BUG=423030

Review URL: https://codereview.chromium.org/653243003

Cr-Commit-Position: refs/heads/master@{#299897}