Make ResourceHandler::OnWillRead able to complete asynchronously.

content/browser/loader/layered_resource_handler.h

Index: content/browser/loader/layered_resource_handler.h
diff --git a/content/browser/loader/layered_resource_handler.h b/content/browser/loader/layered_resource_handler.h
index 0a3846c1cf123800bb98155ead86df1f18ce4ffa..2a714e38da19f53123488d2e7e0526b9a51404ba 100644
--- a/content/browser/loader/layered_resource_handler.h
+++ b/content/browser/loader/layered_resource_handler.h
@@ -37,8 +37,9 @@ class CONTENT_EXPORT LayeredResourceHandler : public ResourceHandler {
       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(