fix($animate): leave animation callback should not overridden by follow-up animation

Closes angular#12271
Closes angular#12249
Closes angular#12161

Author: sreeramu

src/ngAnimate/shared.js

@@ -225,8 +225,16 @@ function mergeAnimationOptions(element, target, newOptions) {
     delete newOptions.preparationClasses;
   }
 
+  // noop is basically when there is no callback; otherwise something has been set
+  var realDomOperation = target.domOperation !== noop ? target.domOperation : null;
+
   extend(target, newOptions);
 
+  // TODO(matsko or sreeramu): proper fix is to maintain all animation callback in array and call at last,but now only leave has the callback so no issue with this.
+  if (realDomOperation) {
+    target.domOperation = realDomOperation;
+  }
+
   if (classes.addClass) {
     target.addClass = classes.addClass;
   } else {

test/ngAnimate/animateSpec.js

@@ -1775,5 +1775,23 @@ describe("animations", function() {
       expect(count).toBe(1);
     }));
 
+    it('leave: should remove the element even if another animation is called after',
+      inject(function($animate, $rootScope, $$rAF, $rootElement) {
+
+      var outerContainer = jqLite('<div></div>');
+      element = jqLite('<div></div>');
+      outerContainer.append(element);
+      $rootElement.append(outerContainer);
+
+      var runner = $animate.leave(element, $rootElement);
+      $animate.removeClass(element,'rclass');
+      $rootScope.$digest();
+      runner.end();
+      $$rAF.flush();
+
+      var isElementRemoved = !outerContainer[0].contains(element[0]);
+      expect(isElementRemoved).toBe(true);
+    }));
+
   });
 });