[Fetch] Support various operations after reading data partially.

Source/modules/serviceworkers/RespondWithObserver.cpp

Index: Source/modules/serviceworkers/RespondWithObserver.cpp
diff --git a/Source/modules/serviceworkers/RespondWithObserver.cpp b/Source/modules/serviceworkers/RespondWithObserver.cpp
index 37ffa42afa8c3e1017836fe3b292afbb20041c01..72a2e545db0c64c8bdf5919f0695f42f0b89cf58 100644
--- a/Source/modules/serviceworkers/RespondWithObserver.cpp
+++ b/Source/modules/serviceworkers/RespondWithObserver.cpp
@@ -203,15 +203,8 @@ void RespondWithObserver::responseWasFulfilled(const ScriptValue& value)
     }
     response->setBodyUsed();
     if (BodyStreamBuffer* buffer = response->internalBuffer()) {
-        if (buffer == response->buffer() && response->streamAccessed()) {
-            bool dataLost = false;
-            buffer = response->createDrainingStream(&dataLost);
-            if (dataLost) {
-                executionContext()->addConsoleMessage(ConsoleMessage::create(JSMessageSource, ErrorMessageLevel, "Returning the stream accessed Response to the page is not supported."));
-                responseWasRejected();
-                return;
-            }
-        }
+        if (buffer == response->buffer() && response->streamAccessed())
+            buffer = response->createDrainingStream();
         WebServiceWorkerResponse webResponse;
         response->populateWebServiceWorkerResponse(webResponse);
         RefPtrWillBeMember<Stream> outStream(Stream::create(executionContext(), ""));