WebMediaRecorder: adding abstract classes to public/platform

public/platform/WebMediaRecorderHandlerClient.h

+// 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 WebMediaRecorderHandlerClient_h
+#define WebMediaRecorderHandlerClient_h
+
+namespace blink {
+
+class WebString;
+
+class WebMediaRecorderHandlerClient {
+public:
+    virtual void writeData(const char* data, size_t length, bool lastInslice) = 0;
+
+    virtual void failOutOfMemory(const WebString& message) = 0;
+    virtual void failIllegalStreamModification(const WebString& message) = 0;
+    virtual void failOtherRecordingError(const WebString& message) = 0;
+
+protected:
+    virtual ~WebMediaRecorderHandlerClient() { }
+};
+
+} // namespace blink
+#endif