[Fetch] Response.clone should tee the body stream.

Source/modules/fetch/Response.cpp

Index: Source/modules/fetch/Response.cpp
diff --git a/Source/modules/fetch/Response.cpp b/Source/modules/fetch/Response.cpp
index 80d47fdb99bb1b5603a79f23f376cf0db2cbc320..f31521ae5233fa696f1694ea162250c8b3c7ab75 100644
--- a/Source/modules/fetch/Response.cpp
+++ b/Source/modules/fetch/Response.cpp
@@ -299,6 +299,10 @@ Response* Response::clone(ExceptionState& exceptionState)
         BodyStreamBuffer* drainingStream = createDrainingStream();
         m_response->replaceBodyStreamBuffer(drainingStream);
     }
+    // Lock the old body and set |body| property to the new one.
+    lockBody();
+    refreshBody();
+
     FetchResponseData* response = m_response->clone();
     Headers* headers = Headers::create(response->headerList());
     headers->setGuard(m_headers->guard());