Add empty 'module' declarations for chrome-devtools

Like: `var SDK = {}`.

These are normally generated by the Chrome dev tools build; adding them
gets rid of more than 10,000 errors

tests/cases/user/chrome-devtools-frontend/definitions.js

@@ -0,0 +1,10 @@
+var Common = {};
+var UI = {};
+var SDK = {};
+var ConsoleModel = {};
+var MobileThrottling = {};
+var Main = {};
+var TimelineModel = {};
+var Accessibility = {};
+var Protocol = {};
+var Workspace = {};