Make FetchDataLoader accept BytesConsumer

third_party/WebKit/Source/modules/fetch/BytesConsumer.h

 // Copyright 2016 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 BytesConsumer_h
 #define BytesConsumer_h
 
 #include "modules/ModulesExport.h"
 #include "platform/blob/BlobData.h"
 #include "platform/heap/Handle.h"
@@ skipping 38 matching lines @@
         bool operator ==(const Error& e) const { return e.m_message == m_message; }
 
     private:
         String m_message;
     };
     // Client gets notification from the associated ByteConsumer.
     class MODULES_EXPORT Client : public GarbageCollectedMixin {
     public:
         virtual ~Client() {}
 
-        // This function is called when the state changes. This function can
-        // be called more than needed, i.e., it can be called even when the
-        // state is not actually changed.
+        // This function is called when the state changes (e.g., readable =>
+        // errored). This function can be called more than needed, i.e., it can
+        // be called even when the state is not actually changed, but it is
+        // guaranteed that this function cannot be called after the state
+        // becomes closed or errored.
         //
         // This function is not called when the state change is trigerred by
         // public methods called by a user. For example, when a user reads
         // data by |read| and the state changes from waiting to readable, this
         // function will not be called.
         virtual void onStateChange() = 0;
     };
 
     virtual ~BytesConsumer() {}
 
@@ skipping 89 matching lines @@
             return PublicState::Errored;
         }
         NOTREACHED();
         return PublicState::ReadableOrWaiting;
     }
 };
 
 } // namespace blink
 
 #endif // BytesConsumer_h