refactor(di): cleanup to make dartanalyzer happy

modules/di/src/reflector.dart

@@ -56,7 +56,8 @@ class Reflector {
   }
 
   List<ParameterMirror> _functionParameters(Function func) {
-    return reflect(func).function.parameters;
+    var closureMirror = reflect(func);
+    return closureMirror.function.parameters;
   }
 
   List<ParameterMirror> _constructorParameters(Type type) {

modules/di/test/di/injector_spec.js

@@ -208,7 +208,7 @@ export function main() {
         bind(Engine).toFactory(() => isBroken ? new BrokenEngine() : new Engine())
       ]);
 
-      expect(() => injector.get(Car)).toThrow();
+      expect(() => injector.get(Car)).toThrowError(new RegExp("Error"));
 
       isBroken = false;