[2a] Implement FetchDataLoader

Source/modules/fetch/FetchDataLoader.h

Index: Source/modules/fetch/FetchDataLoader.h
diff --git a/Source/modules/fetch/FetchDataLoader.h b/Source/modules/fetch/FetchDataLoader.h
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+// Copyright 2015 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 FetchDataLoader_h
+#define FetchDataLoader_h
+
+#include "core/dom/DOMArrayBuffer.h"
+#include "modules/fetch/FetchDataConsumerHandle.h"
+#include "platform/blob/BlobData.h"
+#include "platform/heap/Handle.h"
+#include "wtf/Forward.h"
+
+namespace blink {
+
+// FetchDataLoader subclasses
+// 1. take a reader of FetchDataConsumerHandle |handle|,
+// 2. read all data, and
+// 3. call either didFetchDataLoaded...() on success or
+//    difFetchDataLoadFailed() otherwise
+//    on the thread where FetchDataLoader is created.
+//
+// - Client's methods can be called synchronously in start().
+// - If FetchDataLoader::cancel() is called (or FetchDataLoader is garbage
+//   collected), Client's methods are not called anymore.
+// - FetchDataLoader takes the ownership of |handle|'s reader but not |handle|.
+class FetchDataLoader : public GarbageCollectedFinalized<FetchDataLoader> {
+public:
+    class Client : public GarbageCollectedMixin {
+    public:
+        virtual ~Client() { }
+
+        // The method corresponding to createLoaderAs... is called on success.
+        virtual void didFetchDataLoadedBlobHandle(PassRefPtr<BlobDataHandle>)
+        {
+            ASSERT_NOT_REACHED();
+        }
+        virtual void didFetchDataLoadedArrayBuffer(PassRefPtr<DOMArrayBuffer>)
+        {
+            ASSERT_NOT_REACHED();
+        }
+        virtual void didFetchDataLoadedString(const String&)
+        {
+            ASSERT_NOT_REACHED();
+        }
+
+        virtual void didFetchDataLoadFailed() = 0;
+
+        DEFINE_INLINE_VIRTUAL_TRACE() { }
+    };
+
+    static FetchDataLoader* createLoaderAsBlobHandle(const String& mimeType);
+    static FetchDataLoader* createLoaderAsArrayBuffer();
+    static FetchDataLoader* createLoaderAsString();
+
+    virtual ~FetchDataLoader() { }
+
+    // start() should be called only once on the created thread.
+    // start() do not take the ownership of |handle|.
+    // |handle| must not be locked when called.
+    virtual void start(FetchDataConsumerHandle* /* handle */, Client*) = 0;
+
+    virtual void cancel() = 0;
+
+    DEFINE_INLINE_VIRTUAL_TRACE() { }
+};
+
+} // namespace blink
+
+#endif // FetchDataLoader_h