Remove obviously unneeded forward declarations from headers under src/{app,base,net}.

app/x11_util.h

 // Copyright (c) 2010 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 APP_X11_UTIL_H_
 #define APP_X11_UTIL_H_
 #pragma once
 
 // This file declares utility functions for X11 (Linux only).
 //
 // These functions do not require the Xlib headers to be included (which is why
 // we use a void* for Visual*). The Xlib headers are highly polluting so we try
 // hard to limit their spread into the rest of the code.
 
 #include <string>
 #include <vector>
 
 #include "base/basictypes.h"
 
 typedef struct _GdkDrawable GdkWindow;
 typedef struct _GtkWidget GtkWidget;
 typedef struct _GtkWindow GtkWindow;
 typedef unsigned long XID;
 typedef unsigned long XSharedMemoryId;  // ShmSeg in the X headers.
 typedef struct _XDisplay Display;
 
-namespace base {
-class Thread;
-}
-
 namespace gfx {
 class Rect;
-class Size;
 }
 
 namespace x11_util {
 
 // These functions use the GDK default display and this /must/ be called from
 // the UI thread. Thus, they don't support multiple displays.
 
 // These functions cache their results ---------------------------------
 
 // Check if there's an open connection to an X server.
@@ skipping 133 matching lines @@
 
 // Change desktop for |window| to the desktop of |destination| window.
 bool ChangeWindowDesktop(XID window, XID destination);
 
 // Sets the X Error Handlers so we can catch X errors and crash.
 void SetX11ErrorHandlers();
 
 }  // namespace x11_util
 
 #endif  // APP_X11_UTIL_H_