Add enum to disable reasons for synced extensions.

Just to see if this tickles a perf regression.

BUG=164629,162062


Review URL: https://chromiumcodereview.appspot.com/11522002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@172170 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/chrome/common/extensions/extension.h b/chrome/common/extensions/extension.h
index 9adea8b..19011c18 100644
--- a/chrome/common/extensions/extension.h
+++ b/chrome/common/extensions/extension.h
@@ -121,6 +121,7 @@
     DISABLE_RELOAD = 1 << 2,
     DISABLE_UNSUPPORTED_REQUIREMENT = 1 << 3,
     DISABLE_SIDELOAD_WIPEOUT = 1 << 4,
+    DISABLE_UNKNOWN_FROM_SYNC = 1 << 5,
   };
 
   enum InstallType {