Associate an id with the output surface to handle lost contexts

content/renderer/gpu/mailbox_output_surface.h

Index: content/renderer/gpu/mailbox_output_surface.h
diff --git a/content/renderer/gpu/mailbox_output_surface.h b/content/renderer/gpu/mailbox_output_surface.h
index 0be4712f1d34b2057b8c68adff9a489b275f5fc8..41514300e441df4ce7e1e3ffddfe9d35ca3f16f6 100644
--- a/content/renderer/gpu/mailbox_output_surface.h
+++ b/content/renderer/gpu/mailbox_output_surface.h
@@ -24,6 +24,7 @@ namespace content {
 class MailboxOutputSurface : public CompositorOutputSurface {
  public:
   MailboxOutputSurface(int32 routing_id,
+                       uint32 output_surface_id,
                        WebGraphicsContext3DCommandBufferImpl* context3d,
                        cc::SoftwareOutputDevice* software);
   virtual ~MailboxOutputSurface();
@@ -37,7 +38,8 @@ class MailboxOutputSurface : public CompositorOutputSurface {
 
  private:
   // CompositorOutputSurface overrides.
-  virtual void OnSwapAck(const cc::CompositorFrameAck& ack) OVERRIDE;
+  virtual void OnSwapAck(uint32 output_surface_id,
+                         const cc::CompositorFrameAck& ack) OVERRIDE;
 
   size_t GetNumAcksPending();