Use ExclusiveStreamReader to lock Body.

Source/core/streams/ReadableStream.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef ReadableStream_h
 #define ReadableStream_h
 
 #include "bindings/core/v8/ScriptPromise.h"
 #include "bindings/core/v8/ScriptPromiseProperty.h"
 #include "bindings/core/v8/ScriptState.h"
@@ skipping 51 matching lines @@
     void close();
     void error(PassRefPtrWillBeRawPtr<DOMException>);
 
     void didSourceStart();
 
     // This function is not a getter. It creates an ExclusiveStreamReader and
     // returns it.
     ExclusiveStreamReader* getReader(ExceptionState&);
     // Only ExclusiveStreamReader methods should call this function.
     void setReader(ExclusiveStreamReader*);
+
+    bool isLocked() const { return m_reader; }
     bool isLockedTo(const ExclusiveStreamReader* reader) const { return m_reader == reader; }
 
     bool hasPendingActivity() const override;
     void stop() override;
     DECLARE_VIRTUAL_TRACE();
 
     // Returns the string representation of the given State.
     static String stateToString(State);
 
 protected:
@@ skipping 22 matching lines @@
     Member<WaitPromise> m_ready;
     Member<ClosedPromise> m_closed;
 
     RefPtrWillBeMember<DOMException> m_exception;
     Member<ExclusiveStreamReader> m_reader;
 };
 
 } // namespace blink
 
 #endif // ReadableStream_h