feat: return timeout Id in ZoneTask.toString (fixes #341)

Closes #375

Author: hmdhk

Diff for: lib/zone.ts

@@ -395,6 +395,11 @@ interface TaskData {
    * Delay in milliseconds when the Task will run.
    */
   delay?: number;
+
+  /**
+   * identifier returned by the native setTimeout.
+   */
+  handleId?: number;
 }
 
 /**
@@ -819,6 +824,14 @@ const Zone: ZoneType = (function(global: any) {
         }
       };
     }
+
+  public toString() {
+      if (this.data && typeof this.data.handleId !== 'undefined') {
+        return this.data.handleId;
+      } else {
+        return this.toString();
+      }
+    }
   }
 
   interface UncaughtPromiseError extends Error {

Diff for: test/common/setTimeout.spec.ts

@@ -88,6 +88,12 @@ describe('setTimeout', function () {
     });
   });
 
+  it('should return the timeout Id through toString', function () {
+    var cancelId = setTimeout(() => {
+    }, 0);
+    expect(typeof (cancelId.toString())).toBe('number');
+  })
+
   it('should pass invalid values through', function () {
     clearTimeout(null);
     clearTimeout(<any>{});