Fix platform check in RootWindowController header.

The usage of member variable boot_splash_screen_ 
in root_window_controller.cc file is guarded 
with ChromeOS, while in header it's done with X11. 
This CL replaces X11 platform specific guard in 
header with ChromeOS.

BUG=

Review URL: https://codereview.chromium.org/26168005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227386 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/ash/root_window_controller.h b/ash/root_window_controller.h
index 7820434..f5a67ee 100644
--- a/ash/root_window_controller.h
+++ b/ash/root_window_controller.h
@@ -64,7 +64,7 @@
 class TouchHudProjection;
 class WorkspaceController;
 
-#if defined(USE_X11)
+#if defined(OS_CHROMEOS)
 class BootSplashScreen;
 #endif
 
@@ -259,7 +259,7 @@
   PanelLayoutManager* panel_layout_manager_;
 
   scoped_ptr<SystemBackgroundController> system_background_;
-#if defined(USE_X11)
+#if defined(OS_CHROMEOS)
   scoped_ptr<BootSplashScreen> boot_splash_screen_;
 #endif