Cleanup: Remove unneeded forward declarations in ppapi.

ppapi/cpp/graphics_3d_client.h

 // Copyright (c) 2011 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 PPAPI_CPP_GRAPHICS_3D_CLIENT_H_
 #define PPAPI_CPP_GRAPHICS_3D_CLIENT_H_
 
 #include "ppapi/c/pp_stdint.h"
 
 /// @file
 /// This file defines the API for callbacks related to 3D.
 
 namespace pp {
 
 class Instance;
-class Rect;
-class Scrollbar_Dev;
-class Widget_Dev;
 
 // This class provides a C++ interface for callbacks related to 3D. You
 // would normally use multiple inheritance to derive from this class in your
 // instance.
 class Graphics3DClient {
  public:
   ///
   /// A constructor for creating a Graphics3DClient.
   ///
   /// @param[in] instance The instance that will own the new
   /// <code>Graphics3DClient</code>.
-  Graphics3DClient(Instance* instance);
+  explicit Graphics3DClient(Instance* instance);
 
   /// Destructor.
   virtual ~Graphics3DClient();
 
   /// Graphics3DContextLost() is a notification that the context was lost for
   /// the 3D devices.
   virtual void Graphics3DContextLost() = 0;
 
  private:
   Instance* associated_instance_;
 };
 
 }  // namespace pp
 
-#endif  // PPAPI_CPP_DEV_GRAPHICS_3D_CLIENT_H_
+#endif  // PPAPI_CPP_GRAPHICS_3D_CLIENT_H_