Plumb whether or not a frame is in shadow DOM to the embedder.

public/web/WebFrameClient.h

Index: public/web/WebFrameClient.h
diff --git a/public/web/WebFrameClient.h b/public/web/WebFrameClient.h
index 80281d37ceb1483a4dd388906a833e684f26bc97..425d337ca81b73bb0b4c08c7db6574b060743656 100644
--- a/public/web/WebFrameClient.h
+++ b/public/web/WebFrameClient.h
@@ -55,6 +55,7 @@
 
 namespace blink {
 
+enum class WebTreeScopeType;
 class WebApplicationCacheHost;
 class WebApplicationCacheHostClient;
 class WebAppBannerClient;
@@ -149,6 +150,8 @@ public:
     // until frameDetached() is called on it.
     // Note: If you override this, you should almost certainly be overriding
     // frameDetached().
+    virtual WebFrame* createChildFrame(WebLocalFrame* parent, WebTreeScopeType, const WebString& frameName, WebSandboxFlags sandboxFlags) { return nullptr; }
+    // TODO(dcheng): Remove this overload, since it's deprecated.
     virtual WebFrame* createChildFrame(WebLocalFrame* parent, const WebString& frameName, WebSandboxFlags sandboxFlags) { return nullptr; }
 
     // This frame set its opener to null, disowning it.