Introduce ExclusiveStreamReader.

Source/core/streams/ReadableStream.h

Index: Source/core/streams/ReadableStream.h
diff --git a/Source/core/streams/ReadableStream.h b/Source/core/streams/ReadableStream.h
index 28deb583ab43af3d2ba1556aa53298a3328d3445..36ca2b9267d83db05da82ff46affe4b5df877d8a 100644
--- a/Source/core/streams/ReadableStream.h
+++ b/Source/core/streams/ReadableStream.h
@@ -21,6 +21,7 @@ namespace blink {
 
 class DOMException;
 class ExceptionState;
+class ExclusiveStreamReader;
 class UnderlyingSource;
 
 class ReadableStream : public GarbageCollectedFinalized<ReadableStream>, public ScriptWrappable, public ActiveDOMObject {
@@ -43,31 +44,49 @@ public:
     bool isStarted() const { return m_isStarted; }
     bool isDraining() const { return m_isDraining; }
     bool isPulling() const { return m_isPulling; }
-    State state() const { return m_state; }
-    String stateString() const;
+    State stateInternal() const { return m_state; }
+    DOMException* storedException() { return m_exception.get(); }
 
-    virtual ScriptValue read(ScriptState*, ExceptionState&) = 0;
+    // |stateString|, |read| and |ready| are affected by an exclusive lock. Use
+    // |stateInternal|, |readInternal| and |readyInternal| if you want to avoid
+    // that.
+    String stateString() const;
+    ScriptValue read(ScriptState*, ExceptionState&);
     ScriptPromise ready(ScriptState*);
     ScriptPromise cancel(ScriptState*, ScriptValue reason);
     ScriptPromise closed(ScriptState*);
 
+    virtual ScriptValue readInternal(ScriptState*, ExceptionState&) = 0;
+    ScriptPromise readyInternal(ScriptState*);
+
     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 isLockedTo(const ExclusiveStreamReader* reader) const { return m_reader == reader; }
+
     bool hasPendingActivity() const override;
-    virtual void trace(Visitor*) override;
+    void stop() override;
+    void trace(Visitor*) override;
+
+    // Returns the string representation of the given State.
+    static String stateToString(State);
 
 protected:
     bool enqueuePreliminaryCheck();
     bool enqueuePostAction();
-    void readPreliminaryCheck(ExceptionState&);
-    void readPostAction();
+    void readInternalPreliminaryCheck(ExceptionState&);
+    void readInternalPostAction();
 
 private:
-    typedef ScriptPromiseProperty<Member<ReadableStream>, ToV8UndefinedGenerator, RefPtrWillBeMember<DOMException> > WaitPromise;
-    typedef ScriptPromiseProperty<Member<ReadableStream>, ToV8UndefinedGenerator, RefPtrWillBeMember<DOMException> > ClosedPromise;
+    using WaitPromise = ScriptPromiseProperty<Member<ReadableStream>, ToV8UndefinedGenerator, RefPtrWillBeMember<DOMException>>;
+    using ClosedPromise = ScriptPromiseProperty<Member<ReadableStream>, ToV8UndefinedGenerator, RefPtrWillBeMember<DOMException>>;
 
     virtual bool isQueueEmpty() const = 0;
     virtual void clearQueue() = 0;
@@ -84,7 +103,9 @@ private:
 
     Member<WaitPromise> m_ready;
     Member<ClosedPromise> m_closed;
+
     RefPtrWillBeMember<DOMException> m_exception;
+    Member<ExclusiveStreamReader> m_reader;
 };
 
 } // namespace blink