Eliminate MediaPlayer & MediaPlayerClient abstractions

Source/platform/exported/WebMediaPlayerClient.cpp

Index: Source/platform/exported/WebMediaPlayerClient.cpp
diff --git a/Source/platform/exported/WebMediaPlayerClient.cpp b/Source/platform/exported/WebMediaPlayerClient.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..bd78907fa9ffec7db8e439882048224352a4bdc4
--- /dev/null
+++ b/Source/platform/exported/WebMediaPlayerClient.cpp
@@ -0,0 +1,13 @@
+// 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.
+
+#include "config.h"
+#include "public/platform/WebMediaPlayerClient.h"
+
+// This WebMediaPlayerClient.cpp, which includes only config.h
+// and WebMediaPlayerClient.h, should be in
+// Source/platform/exported, because WebMediaPlayerClient is not
+// compiled without this cpp.
+// So if we don't have this cpp, we will see unresolved symbol error
+// when constructor/destructor's address is required.