mac: Suppress partial availability warnings in theme helper.

content/browser/theme_helper_mac.mm

Index: content/browser/theme_helper_mac.mm
diff --git a/content/browser/theme_helper_mac.mm b/content/browser/theme_helper_mac.mm
index 29190602f8dcc9c756446507b330f86da4c7999c..3abe515d4fd6028fe6eddb6b64386a990e1610c6 100644
--- a/content/browser/theme_helper_mac.mm
+++ b/content/browser/theme_helper_mac.mm
@@ -15,15 +15,6 @@
 #include "content/public/browser/render_process_host.h"
 #include "content/public/common/content_switches.h"
 
-// Declare notification names from the 10.7 SDK.
-#if !defined(MAC_OS_X_VERSION_10_7) || \
-    MAC_OS_X_VERSION_MAX_ALLOWED < MAC_OS_X_VERSION_10_7
-
-NSString* NSPreferredScrollerStyleDidChangeNotification =
-    @"NSPreferredScrollerStyleDidChangeNotification";
-
-#endif
-
 @interface ScrollbarPrefsObserver : NSObject
 
 + (void)registerAsObserver;