fix($injector): add workaround for class stringification in Chrome v50/51

Partially fixes angular#14240.

Author: gkalpak

src/auto/injector.js

@@ -70,12 +70,16 @@ var FN_ARG = /^\s*(_?)(\S+?)\1\s*$/;
 var STRIP_COMMENTS = /((\/\/.*$)|(\/\*[\s\S]*?\*\/))/mg;
 var $injectorMinErr = minErr('$injector');
 
-function extractArgs(fn) {
+function stringifyFn(fn) {
   // Support: Chrome 50-51 only
   // Creating a new string by adding `' '` at the end, to hack around some bug in Chrome v50/51
   // (See https://github.com/angular/angular.js/issues/14487.)
   // TODO (gkalpak): Remove workaround when Chrome v52 is released
-  var fnText = Function.prototype.toString.call(fn).replace(STRIP_COMMENTS, '') + ' ',
+  return Function.prototype.toString.call(fn) + ' ';
+}
+
+function extractArgs(fn) {
+  var fnText = stringifyFn(fn).replace(STRIP_COMMENTS, ''),
       args = fnText.match(ARROW_ARG) || fnText.match(FN_ARGS);
   return args;
 }
@@ -849,7 +853,7 @@ function createInjector(modulesToLoad, strictDi) {
       if (!isBoolean(result)) {
         // Workaround for MS Edge.
         // Check https://connect.microsoft.com/IE/Feedback/Details/2211653
-        result = func.$$ngIsClass = /^(?:class\s|constructor\()/.test(Function.prototype.toString.call(func));
+        result = func.$$ngIsClass = /^(?:class\s|constructor\()/.test(stringifyFn(func));
       }
       return result;
     }

test/auto/injectorSpec.js

@@ -283,6 +283,14 @@ describe('injector', function() {
         it('should take args before first arrow', function() {
           expect(annotate(eval('a => b => b'))).toEqual(['a']);
         });
+
+        // Support: Chrome 50-51 only
+        // TODO (gkalpak): Remove when Chrome v52 is relased.
+        // it('should be able to inject fat-arrow function', function() {
+        //   inject(($injector) => {
+        //     expect($injector).toBeDefined();
+        //   });
+        // });
       }
 
       if (support.classes) {
@@ -293,6 +301,19 @@ describe('injector', function() {
           expect(instance).toEqual(new Clazz('a-value'));
           expect(instance.aVal()).toEqual('a-value');
         });
+
+        // Support: Chrome 50-51 only
+        // TODO (gkalpak): Remove when Chrome v52 is relased.
+        // it('should be able to invoke classes', function() {
+        //   class Test {
+        //     constructor($injector) {
+        //       this.$injector = $injector;
+        //     }
+        //   }
+        //   var instance = injector.invoke(Test, null, null, 'Test');
+
+        //   expect(instance.$injector).toBe(injector);
+        // });
       }
       /*jshint +W061 */
     });