fix($compile): set attribute value even if ngAttr* contains no interpolation

Previoulsy, when the value of an `ngAttrXyz` attribute did not contain any interpolation, then the
`xyz` attribute was never set.

BTW, this commit adds a negligible overhead (since we have to set up a one-time watcher for
example), but it is justifiable for someone that is using `ngAttrXyz` (instead of `xyz` directly).

Fixes angular#15133

Author: gkalpak

src/ng/compile.js

@@ -3251,16 +3251,16 @@ function $CompileProvider($provide, $$sanitizeUriProvider) {
     }
 
 
-    function addAttrInterpolateDirective(node, directives, value, name, allOrNothing) {
+    function addAttrInterpolateDirective(node, directives, value, name, isNgAttr) {
       var trustedContext = getTrustedContext(node, name);
-      allOrNothing = ALL_OR_NOTHING_ATTRS[name] || allOrNothing;
+      var mustHaveExpression = !isNgAttr;
+      var allOrNothing = ALL_OR_NOTHING_ATTRS[name] || isNgAttr;
 
-      var interpolateFn = $interpolate(value, true, trustedContext, allOrNothing);
+      var interpolateFn = $interpolate(value, mustHaveExpression, trustedContext, allOrNothing);
 
       // no interpolation found -> ignore
       if (!interpolateFn) return;
 
-
       if (name === 'multiple' && nodeName_(node) === 'select') {
         throw $compileMinErr('selmulti',
             'Binding to the \'multiple\' attribute is not supported. Element: {0}',

test/ng/compileSpec.js

@@ -11185,6 +11185,14 @@ describe('$compile', function() {
       expect(element.attr('test')).toBe('Misko');
     }));
 
+    it('should set the attribute (after digest) even if there is no interpolation', inject(function() {
+      element = $compile('<span ng-attr-test="foo"></span>')($rootScope);
+      expect(element.attr('test')).toBeUndefined();
+
+      $rootScope.$digest();
+      expect(element.attr('test')).toBe('foo');
+    }));
+
     it('should remove attribute if any bindings are undefined', inject(function() {
       element = $compile('<span ng-attr-test="{{name}}{{emphasis}}"></span>')($rootScope);
       $rootScope.$digest();