ResizingHostObserver is created by the desktop environment together with other stubs.

remoting/host/session_controller.h

Index: remoting/host/session_controller.h
diff --git a/remoting/host/session_controller.h b/remoting/host/session_controller.h
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index 0000000000000000000000000000000000000000..46fff8ddbdae29ccc4d85ae526d85ed5af60be3e
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+++ b/remoting/host/session_controller.h
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+// Copyright (c) 2013 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 REMOTING_HOST_SESSION_CONTROLLER_H_
+#define REMOTING_HOST_SESSION_CONTROLLER_H_
+
+#include "base/basictypes.h"
+#include "third_party/skia/include/core/SkPoint.h"
+#include "third_party/skia/include/core/SkSize.h"
+
+namespace remoting {
+
+class SessionController {
+ public:
+  virtual ~SessionController() {}
+
+  // Called when the client view size or pixel density change.
+  virtual void OnClientResolutionChanged(const SkIPoint& client_dpi,
+                                         const SkISize& client_size) = 0;
+};
+
+}  // namespace remoting
+
+#endif  // REMOTING_HOST_SESSION_CONTROLLER_H_