refactor(facade): Inline isBlank called with object-type argument (#11992)

modules/@angular/http/src/headers.ts

@@ -7,7 +7,6 @@
  */
 
 import {ListWrapper, MapWrapper, StringMapWrapper, isListLikeIterable, iterateListLike} from '../src/facade/collection';
-import {isBlank} from '../src/facade/lang';
 
 /**
  * Polyfill for [Headers](https://developer.mozilla.org/en-US/docs/Web/API/Headers/Headers), as
@@ -48,7 +47,7 @@ export class Headers {
 
     this._headersMap = new Map<string, string[]>();
 
-    if (isBlank(headers)) {
+    if (!headers) {
       return;
     }