Support global keyboard commands on Chrome OS.

chrome/test/data/extensions/api_test/keybinding/global/manifest.json

 {
   "name": "An extension to test global shortcuts",
   "version": "1.0",
   "manifest_version": 2,
   "background": {
     "scripts": ["background.js"]
   },
   "commands": {
     "Ctrl-Shift-1-non-global": {
       "suggested_key": {
         "default": "Ctrl+Shift+1"
       },      
       "description": "Test fails if called (non-global)"
     },
     "Ctrl-Shift-A-Non-Assignable-Globally": {
       "suggested_key": {
         "default": "Ctrl+Shift+A"
       },      
       "description":
           "Test fails if called (Ctrl+Shift+A not auto-assignable globally)",
       "global": true
     },
-    "Ctrl-Shift-9-Valid-Global-Shortcut": {
+    "Ctrl-Shift-8-Valid-Global-Shortcut": {
       "suggested_key": {
-        "default": "Ctrl+Shift+9"
+        "default": "Ctrl+Shift+8"
       },
       "description": "Test passes if called (global shortcut)",
       "global": true
     }
   }
 }