Add AshDesktopMediaList and enable Desktop Capture API on Chrome OS.

content/browser/renderer_host/media/desktop_capture_device_aura.cc

Index: content/browser/renderer_host/media/desktop_capture_device_aura.cc
diff --git a/content/browser/renderer_host/media/desktop_capture_device_aura.cc b/content/browser/renderer_host/media/desktop_capture_device_aura.cc
index a36d26b8b5f8955646ba33964c72a9e55a133769..15e86f0323ba9008d4343158284d088d587c120e 100644
--- a/content/browser/renderer_host/media/desktop_capture_device_aura.cc
+++ b/content/browser/renderer_host/media/desktop_capture_device_aura.cc
@@ -217,14 +217,17 @@ void DesktopVideoCaptureMachine::Stop() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
   // Stop observing window events.
-  if (desktop_window_)
+  if (desktop_window_) {
     desktop_window_->RemoveObserver(this);
+    desktop_window_ = NULL;
+  }
 
   // Stop observing compositor updates.
   if (desktop_layer_) {
     ui::Compositor* compositor = desktop_layer_->GetCompositor();
     if (compositor)
       compositor->RemoveObserver(this);
+    desktop_layer_ = NULL;
   }
 
   // Stop timer.
@@ -290,7 +293,7 @@ void DesktopVideoCaptureMachine::DidCopyOutput(
     base::Time start_time,
     const ThreadSafeCaptureOracle::CaptureFrameCallback& capture_frame_cb,
     scoped_ptr<cc::CopyOutputResult> result) {
-  if (result->IsEmpty() || result->size().IsEmpty())
+  if (result->IsEmpty() || result->size().IsEmpty() || !desktop_layer_)
     return;
 
   // Compute the dest size we want after the letterboxing resize. Make the
@@ -396,13 +399,11 @@ void DesktopVideoCaptureMachine::OnWindowBoundsChanged(
 }
 
 void DesktopVideoCaptureMachine::OnWindowDestroyed(aura::Window* window) {
-  DCHECK(desktop_window_ && window == desktop_window_);
-  desktop_window_ = NULL;
-  desktop_layer_ = NULL;
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
-  // Post task to stop capture on UI thread.
-  BrowserThread::PostTask(BrowserThread::UI, FROM_HERE, base::Bind(
-      &DesktopVideoCaptureMachine::Stop, AsWeakPtr()));
+  Stop();
+
+  oracle_proxy_->ReportError();
 }
 
 void DesktopVideoCaptureMachine::OnCompositingEnded(