fix($rootScope): don't allow explicit digest calls to affect $evalAsync

Fixes #15127

Closes #15494

Author: dcherman

src/ng/rootScope.js

@@ -772,7 +772,7 @@ function $RootScopeProvider() {
         var watch, value, last, fn, get,
             watchers,
             dirty, ttl = TTL,
-            next, current, target = this,
+            next, current, target = asyncQueue.length ? $rootScope : this,
             watchLog = [],
             logIdx, asyncTask;
 

test/ng/rootScopeSpec.js

@@ -2142,6 +2142,25 @@ describe('Scope', function() {
         $browser.defer.flush(100000);
         expect(log).toEqual(['eval-ed 1!', 'eval-ed 2!']);
       });
+
+      it('should not have execution affected by an explicit $digest call', function() {
+        var scope1 = $rootScope.$new();
+        var scope2 = $rootScope.$new();
+
+        scope1.$watch('value', function(value) {
+          scope1.result = value;
+        });
+
+        scope1.$evalAsync(function() {
+          scope1.value = 'bar';
+        });
+
+        scope2.$digest();
+
+        $browser.defer.flush(0);
+
+        expect(scope1.result).toBe('bar');
+      });
     });
 
     it('should not pass anything as `this` to scheduled functions', inject(function($rootScope) {