Move kDisableCoreAnimationPlugins to content_switches since it's only used in content now.

ui/base/ui_base_switches.cc

Index: ui/base/ui_base_switches.cc
===================================================================
--- ui/base/ui_base_switches.cc	(revision 216744)
+++ ui/base/ui_base_switches.cc	(working copy)
@@ -98,13 +98,6 @@
 const char kTouchCalibration[] = "touch-calibration";
 #endif
 
-#if defined(OS_MACOSX)
-// Disables support for Core Animation plugins. This is triggered when
-// accelerated compositing is disabled. See http://crbug.com/122430 .
-const char kDisableCoreAnimationPlugins[] =
-    "disable-core-animation-plugins";
-#endif
-
 #if defined(TOOLKIT_VIEWS) && defined(OS_LINUX)
 // Tells chrome to interpret events from these devices as touch events. Only
 // available with XInput 2 (i.e. X server 1.8 or above). The id's of the