feat(ngModelOptions): allow options to be inherited from ancestor ngModelOptions

Previously, you had to apply the complete set of `ngModelOptions` at every point where
you might want to modify just one or two settings.

This change allows more general settings to be applied nearer to the top of the DOM
and then for more specific settings to override those general settings further down
in the DOM.

To prevent unwanted inheritance you must opt-in on a case by case basis:
* To inherit as single property you simply provide the special value `"$inherit"`.
* To inherit all properties not specified locally then include a property `"*": "$inherit"`.

Closes angular#10922
Closes angular#15389

BREAKING CHANGE:

The programmatic API for `ngModelOptions` has changed. You must now read options
via the `ngModelController.getOption(name)` method, rather than accessing the option directly as a property
of the `ngModelContoller.$options` object. This does not affect the usage in templates and only
affects custom directives that might have been reading options for their own purposes.

Author: petebacondarwin

src/ng/directive/ngModelOptions.js

@@ -47,13 +47,21 @@ ModelOptions.prototype = {
           inheritAll = true;
         } else {
           options[key] = this.$$options[key];
+          // `updateOn` is special so we must also inherit the `updateOnDefault` option
+          if (key === 'updateOn') {
+            options.updateOnDefault = this.$$options.updateOnDefault;
+          }
+        }
+      } else {
+        if (key === 'updateOn') {
+          // If the `updateOn` property contains the `default` event then we have to remove
+          // it from the event list and set the `updateOnDefault` flag.
+          options.updateOnDefault = false;
+          options[key] = trim(option.replace(DEFAULT_REGEXP, function() {
+            options.updateOnDefault = true;
+            return ' ';
+          }));
         }
-      } else if (key === 'updateOn') {
-        options.updateOnDefault = false;
-        options[key] = trim(option.replace(DEFAULT_REGEXP, function() {
-          options.updateOnDefault = true;
-          return ' ';
-        }));
       }
     }, this);
 

test/ng/directive/ngModelOptionsSpec.js

@@ -180,6 +180,31 @@ describe('ngModelOptions', function() {
       });
 
 
+      it('should `updateOnDefault` as well if we have `updateOn: "$inherit"`', function() {
+        var container = $compile(
+                  '<div ng-model-options="{updateOn: \'keyup\'}">' +
+                    '<input ng-model-options="{updateOn: \'$inherit\'}">' +
+                    '<div ng-model-options="{updateOn: \'default blur\'}">' +
+                      '<input ng-model-options="{updateOn: \'$inherit\'}">' +
+                    '</div>' +
+                  '</div>')($rootScope);
+
+        var input1 = container.find('input').eq(0);
+        var inputOptions1 = input1.controller('ngModelOptions').$options;
+
+        expect(inputOptions1.getOption('updateOn')).toEqual('keyup');
+        expect(inputOptions1.getOption('updateOnDefault')).toEqual(false);
+
+        var input2 = container.find('input').eq(1);
+        var inputOptions2 = input2.controller('ngModelOptions').$options;
+
+        expect(inputOptions2.getOption('updateOn')).toEqual('blur');
+        expect(inputOptions2.getOption('updateOnDefault')).toEqual(true);
+
+        dealoc(container);
+      });
+
+
       it('should make a copy of the options object', function() {
         $rootScope.options = {updateOn: 'default'};
         var inputElm = helper.compileInput(