feat(facade): add support for all thenables (#10278)

All objects that have a then function will be considered Promises

modules/@angular/facade/src/lang.ts

@@ -133,7 +133,9 @@ export function isStrictStringMap(obj: any): boolean {
 }
 
 export function isPromise(obj: any): boolean {
-  return obj instanceof (<any>_global).Promise;
+  // allow any Promise/A+ compliant thenable.
+  // It's up to the caller to ensure that obj.then conforms to the spec
+  return isPresent(obj) && isFunction(obj.then);
 }
 
 export function isArray(obj: any): boolean {

modules/@angular/facade/test/lang_spec.ts

@@ -6,7 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {NumberWrapper, RegExpMatcherWrapper, RegExpWrapper, StringWrapper, escapeRegExp, hasConstructor, isPresent, resolveEnumToken} from '../src/lang';
+import {NumberWrapper, RegExpMatcherWrapper, RegExpWrapper, StringWrapper, escapeRegExp, hasConstructor, isPresent, isPromise, resolveEnumToken} from '../src/lang';
 
 enum UsefulEnum {
   MyToken,
@@ -184,4 +184,22 @@ export function main() {
          () => { expect(hasConstructor(new MySubclass(), MySuperclass)).toEqual(false); });
     });
   });
+  describe('isPromise', () => {
+    it('should be true for native Promises',
+       () => expect(isPromise(Promise.resolve(true))).toEqual(true));
+
+    it('should be true for thenables',
+       () => expect(isPromise({then: function() {}})).toEqual(true));
+
+    it('should be false if "then" is not a function',
+       () => expect(isPromise({then: 0})).toEqual(false));
+
+    it('should be false if the argument has no "then" function',
+       () => expect(isPromise({})).toEqual(false));
+
+    it('should be false if the argument is undefined or null', () => {
+      expect(isPromise(undefined)).toEqual(false);
+      expect(isPromise(null)).toEqual(false);
+    });
+  });
 }