feat(injector): add has method for querying

Closes #2556

src/auto/injector.js

@@ -597,7 +597,10 @@ function createInjector(modulesToLoad) {
       invoke: invoke,
       instantiate: instantiate,
       get: getService,
-      annotate: annotate
+      annotate: annotate,
+      has: function(name) {
+        return providerCache.hasOwnProperty(name + providerSuffix) || cache.hasOwnProperty(name);
+      }
     };
   }
 }

src/ng/animation.js

@@ -51,13 +51,9 @@ function $AnimationProvider($provide) {
      */
     return function $animation(name) {
       if (name) {
-        try {
-          return $injector.get(camelCase(name) + suffix);
-        } catch (e) {
-          //TODO(misko): this is a hack! we should have a better way to test if the injector has a given key.
-          // The issue is that the animations are optional, and if not present they should be silently ignored.
-          // The proper way to fix this is to add API onto the injector so that we can ask to see if a given
-          // animation is supported.
+        var animationName = camelCase(name) + suffix;
+        if ($injector.has(animationName)) {
+          return $injector.get(animationName);
         }
       }
     }

test/auto/injectorSpec.js

@@ -58,6 +58,15 @@ describe('injector', function() {
   });
 
 
+  it('should allow query names', function() {
+    providers('abc', function () { return ''; });
+
+    expect(injector.has('abc')).toBe(true);
+    expect(injector.has('xyz')).toBe(false);
+    expect(injector.has('$injector')).toBe(true);
+  });
+
+
   it('should provide useful message if no provider', function() {
     expect(function() {
       injector.get('idontexist');