Expose Frame::detach() to the Blink API layer.

public/web/WebRemoteFrameClient.h

Index: public/web/WebRemoteFrameClient.h
diff --git a/public/web/WebRemoteFrameClient.h b/public/web/WebRemoteFrameClient.h
index 06ef91fc9f7dbf98bf00774aa407e825ff83208f..c74be26e57ee5e6cf12d66bfa17aedd80b3c5f41 100644
--- a/public/web/WebRemoteFrameClient.h
+++ b/public/web/WebRemoteFrameClient.h
@@ -14,6 +14,10 @@ class WebRemoteFrame;
 
 class WebRemoteFrameClient {
 public:
+    // Notify the embedder that it should remove this frame from the frame tree
+    // and release any resources associated with it.
+    virtual void frameDetached() { }
+
     // Notifies the embedder that a postMessage was issued to a remote frame.
     virtual void postMessageEvent(
         WebLocalFrame* sourceFrame,