Make ResourceHandler::OnWillRead able to complete asynchronously.

content/browser/loader/mojo_async_resource_handler.h

Index: content/browser/loader/mojo_async_resource_handler.h
diff --git a/content/browser/loader/mojo_async_resource_handler.h b/content/browser/loader/mojo_async_resource_handler.h
index 4dd975c80a9da001cbbb5b8c999f7539b350bc95..cb8ca4e870ebca5f6be7512d87f022ac1e4abedd 100644
--- a/content/browser/loader/mojo_async_resource_handler.h
+++ b/content/browser/loader/mojo_async_resource_handler.h
@@ -70,8 +70,9 @@ class CONTENT_EXPORT MojoAsyncResourceHandler
       std::unique_ptr<ResourceController> controller) override;
   void OnWillStart(const GURL& url,
                    std::unique_ptr<ResourceController> controller) override;
-  bool OnWillRead(scoped_refptr<net::IOBuffer>* buf,
-                  int* buf_size) override;
+  void OnWillRead(scoped_refptr<net::IOBuffer>* buf,
+                  int* buf_size,
+                  std::unique_ptr<ResourceController> controller) override;
   void OnReadCompleted(int bytes_read,
                        std::unique_ptr<ResourceController> controller) override;
   void OnResponseCompleted(