Limit extensions to 1 UI surface (either Page/Browser action, but not both)....

chrome/common/extensions/extension_constants.cc

Index: chrome/common/extensions/extension_constants.cc
===================================================================
--- chrome/common/extensions/extension_constants.cc	(revision 29153)
+++ chrome/common/extensions/extension_constants.cc	(working copy)
@@ -167,6 +167,8 @@
     "Invalid value for update url: '[*]'.";
 const char* kInvalidDefaultLocale =
     "Invalid value for default locale - locale name must be a string.";
+const char* kOneUISurfaceOnly =
+    "An extension cannot have both a page action and a browser action.";
 const char* kThemesCannotContainExtensions =
     "A theme cannot contain extensions code.";
 const char* kLocalesNoDefaultLocaleSpecified =