[Fetch] Support various operations after reading data partially.

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 25a33948a6c980c56f0d14ae610b32391fffabf8..6e43fbcf9cd354d441b3436c981033062925f861 100644
--- a/Source/modules/fetch/Response.cpp
+++ b/Source/modules/fetch/Response.cpp
@@ -301,17 +301,8 @@ Response* Response::clone(ExceptionState& exceptionState)
         exceptionState.throwTypeError("Response body is already used");
         return nullptr;
     }
-    // FIXME: We throw an error while cloning the Response which body was
-    // partially read. But in Request case, we don't. When the behavior of the
-    // partially read streams will be well defined in the spec, we have to
-    // implement the behavior correctly.
     if (streamAccessed()) {
-        bool dataLost = false;
-        BodyStreamBuffer* drainingStream = createDrainingStream(&dataLost);
-        if (dataLost) {
-            exceptionState.throwTypeError("Cloning the Response which body was partially read is not supported.");
-            return nullptr;
-        }
+        BodyStreamBuffer* drainingStream = createDrainingStream();
         m_response->replaceBodyStreamBuffer(drainingStream);
     }
     return Response::createClone(*this);