Let canvas decide how to handle the case of resource lost reported by client: 2D part

public/platform/WebExternalTextureLayerClient.h

Index: public/platform/WebExternalTextureLayerClient.h
diff --git a/public/platform/WebExternalTextureLayerClient.h b/public/platform/WebExternalTextureLayerClient.h
index 148e63ffb9dd171d3f7c8ff6e83958e7d9a8a268..bfce0e27f3869c0f4bfd81e39913157202e6becb 100644
--- a/public/platform/WebExternalTextureLayerClient.h
+++ b/public/platform/WebExternalTextureLayerClient.h
@@ -43,8 +43,11 @@ public:
     virtual bool prepareMailbox(WebExternalTextureMailbox*, WebExternalBitmap* = 0) = 0;
 
     // Notifies the client when a mailbox is no longer in use by the compositor and provides
-    // a sync point to wait on before the mailbox could be consumes again by the client.
-    virtual void mailboxReleased(const WebExternalTextureMailbox&) = 0;
+    // a sync point to wait on before the mailbox could be consumes again by the client. The
+    // boolean flag indicates if the mailbox resource is treated as lost by client.
+    // FIXME(hmin): Remove the default value for lostResource once the chromium part CL at
+    // https://codereview.chromium.org/369823002 is landed.
+    virtual void mailboxReleased(const WebExternalTextureMailbox&, bool lostResource = false) = 0;
 
 protected:
     virtual ~WebExternalTextureLayerClient() { }