perf($rootScope): do not mark the $watchCollection interceptor $stateful

... for literal expressions

Author: jbedard

src/ng/rootScope.js

@@ -581,7 +581,10 @@ function $RootScopeProvider() {
        *    de-registration function is executed, the internal watch operation is terminated.
        */
       $watchCollection: function(obj, listener) {
-        $watchCollectionInterceptor.$stateful = true;
+        // Mark it as $stateful to avoid any input-watching and always invoke the interceptor
+        // since the inputs will most likely be non-simple (like collections!).
+        // ... unless it is a literal and input-watching may be sufficient.
+        $watchCollectionInterceptor.$stateful = !$parse(obj).literal;
 
         var self = this;
         // the current value, updated on each dirty-check run