Remove unused WebURLRequestExtraData class

sky/viewer/platform/weburlloader_impl.h

Index: sky/viewer/platform/weburlloader_impl.h
diff --git a/sky/viewer/platform/weburlloader_impl.h b/sky/viewer/platform/weburlloader_impl.h
index a8573cd3f602f8a3352009d8086bc12130992a7f..3372f437467a610ab248768b58191533df5d9da5 100644
--- a/sky/viewer/platform/weburlloader_impl.h
+++ b/sky/viewer/platform/weburlloader_impl.h
@@ -16,14 +16,6 @@ class NetworkService;
 }
 
 namespace sky {
-// The concrete type of WebURLRequest::ExtraData.
-class WebURLRequestExtraData : public blink::WebURLRequest::ExtraData {
- public:
-  WebURLRequestExtraData();
-  virtual ~WebURLRequestExtraData();
-
-  mojo::URLResponsePtr synthetic_response;
-};
 
 class WebURLLoaderImpl : public blink::WebURLLoader {
  public: