fix: Canceling already run task should not double decrement task counter

Closes #290

lib/browser/browser.ts

@@ -86,7 +86,10 @@ function patchTimer(
   var clearNative = patchMethod(window, cancelName, (delegate: Function) => function(self: any, args: any[]) {
     var task: Task = args[0];
     if (task && typeof task.type == 'string') {
-      task.zone.cancelTask(task);
+      if (task.cancelFn) {
+        // Do not cancel already canceled functions
+        task.zone.cancelTask(task);
+      }
     } else {
       // cause an error by calling it directly.
       delegate.apply(window, args);

lib/zone.ts

@@ -581,11 +581,11 @@ var Zone: ZoneType = (function(global) {
           }
         }
       } finally {
+        if (task.type == 'macroTask' && task.data && !task.data.isPeriodic) {
+          task.cancelFn = null;
+        }
         _currentZone = oldZone;
         _currentTask = previousTask;
-        if (task.type == 'microTask') {
-
-        }
       }
     }
 
@@ -761,7 +761,6 @@ var Zone: ZoneType = (function(global) {
       var prev = counts[type];
       var next = counts[type] = prev + count;
       if (next < 0) {
-        debugger;
         throw new Error('More tasks executed then were scheduled.');
       }
       if (prev == 0 || next == 0) {

test/browser/setTimeout.spec.ts

@@ -40,6 +40,18 @@ describe('setTimeout', function () {
     });
   });
 
+  it('should allow double cancelation of fns registered with setTimeout', function (done) {
+    var spy = jasmine.createSpy('spy');
+    var cancelId = setTimeout(spy, 0);
+    setTimeout(function () {
+      expect(spy).toHaveBeenCalled();
+      setTimeout(function () {
+        clearTimeout(cancelId);
+        done();
+      });
+    });
+  });
+
   it('should pass invalid values through', function () {
     clearTimeout(null);
     clearTimeout(<any>{});