Introduce WebDataConsumerHandle.

public/platform/WebDataConsumerHandle.h

Index: public/platform/WebDataConsumerHandle.h
diff --git a/public/platform/WebDataConsumerHandle.h b/public/platform/WebDataConsumerHandle.h
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+// 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 WebDataConsumerHandle_h
+#define WebDataConsumerHandle_h
+
+#include <stddef.h>
+
+namespace blink {
+
+// WebDataConsumerHandle represents the "consumer" side of a data pipe. A user
+// can read data from it.
+// This data type is basically a wrapper of mojo data pipe consumer handle.
+// See mojo/public/c/system/data_pipe.h for details.
+//
+// Note:
+//  - If you register a client, all of read / beginRead / endRead /
+//    registerClient / unregisterClient must be called on the same thread.
+//    Client notification is called on the thread.
+class WebDataConsumerHandle {
+public:
+    // This corresponds to MojoReadDataFlags.
+    using Flags = unsigned;
+    static const Flags FlagNone = 0;
+
+    enum Result {
+        Ok,
+        Done,
+        Busy,
+        ShouldWait,
+        ResourceExhausted,
+        UnexpectedError,
+    };
+
+    // Client gets notification from the pipe.
+    class Client {
+    public:
+        virtual ~Client() { }
+        // The associated handle gets readable.
+        virtual void didGetReadable() = 0;
+    };
+
+    virtual ~WebDataConsumerHandle() { }
+
+    // Reads data into |data| up to |size| bytes. The actual read size will be
+    // stored in |*readSize|. This function cannot be called when a two-phase
+    // read is in progress.
+    // Returns Done when it reaches to the end of the data.
+    virtual Result read(void* data, size_t /* size */, Flags, size_t* readSize) { return UnexpectedError; }
+
+    // Begins a two-phase read. On success, the function stores a buffer that
+    // contains the read data of length |*available| into |*buffer|.
+    // Returns Done when it reaches to the end of the data.
+    // On fail, you don't have to (and should not) call endRead, because the
+    // read session implicitly ends in that case.
+    virtual Result beginRead(const void** buffer, Flags, size_t* available) { return UnexpectedError; }
+
+    // Ends a two-phase read.
+    // |readSize| indicates the actual read size.
+    virtual Result endRead(size_t readSize) { return UnexpectedError; }
+
+    // Registers |client| to this handle. The client must not be null and must
+    // be valid until it is unregistered (or the handle is destructed).
+    // Only one registration can be made for a handle at a time.
+    virtual void registerClient(Client* /* client */)  { }
+
+    // Unregisters |client| from this handle.
+    virtual void unregisterClient() { }
+};
+
+} // namespace blink
+
+#endif // WebDataConsumerHandle_h