feat($rootScope): allow for a scope to have partialDigest

When a scope has partialDigest, $apply-ing the scope
only triggers the dirty checking in that scope and its descendants

BREAKING CHANGE:
Scope.$apply now requires its `this` to be a given scope.

Replace any calls similar to
```js
expect($rootScope.$apply).toThrow('...')
```
with
```js
expect(function () {
  $rootScope.$apply();
}).toThrow('...');
```

Author: rodyhaddad

src/ng/rootScope.js

@@ -134,6 +134,7 @@ function $RootScopeProvider(){
       this.$$listeners = {};
       this.$$listenerCount = {};
       this.$$isolateBindings = {};
+      this.$$digestTarget = true;
     }
 
     /**
@@ -170,7 +171,7 @@ function $RootScopeProvider(){
        * @returns {Object} The newly created child scope.
        *
        */
-      $new: function(isolate) {
+      $new: function(isolate, partialDigest) {
         var ChildScope,
             child;
 
@@ -205,6 +206,7 @@ function $RootScopeProvider(){
         } else {
           this.$$childHead = this.$$childTail = child;
         }
+        child.$$digestTarget = !!partialDigest;
         return child;
       },
 
@@ -976,7 +978,9 @@ function $RootScopeProvider(){
         } finally {
           clearPhase();
           try {
-            $rootScope.$digest();
+            var scope = this;
+            while(!scope.$$digestTarget) scope = scope.$parent;
+            scope.$digest();
           } catch (e) {
             $exceptionHandler(e);
             throw e;

test/ng/compileSpec.js

@@ -3014,7 +3014,7 @@ describe('$compile', function() {
         expect(componentScope.ref).toBe('hello world');
 
         componentScope.ref = 'ignore me';
-        expect($rootScope.$apply).
+        expect(function() {$rootScope.$apply(); }).
             toThrowMinErr("$compile", "nonassign", "Expression ''hello ' + name' used with directive 'myComponent' is non-assignable!");
         expect(componentScope.ref).toBe('hello world');
         // reset since the exception was rethrown which prevented phase clearing
@@ -5180,7 +5180,7 @@ describe('$compile', function() {
       /* jshint scripturl:true */
       element = $compile('<iframe src="{{testUrl}}"></iframe>')($rootScope);
       $rootScope.testUrl = $sce.trustAsUrl("javascript:doTrustedStuff()");
-      expect($rootScope.$apply).toThrowMinErr(
+      expect(function() {$rootScope.$apply(); }).toThrowMinErr(
           "$interpolate", "interr", "Can't interpolate: {{testUrl}}\nError: [$sce:insecurl] Blocked " +
           "loading resource from url not allowed by $sceDelegate policy.  URL: javascript:doTrustedStuff()");
     }));
@@ -5226,7 +5226,7 @@ describe('$compile', function() {
       /* jshint scripturl:true */
       element = $compile('<form action="{{testUrl}}"></form>')($rootScope);
       $rootScope.testUrl = $sce.trustAsUrl("javascript:doTrustedStuff()");
-      expect($rootScope.$apply).toThrowMinErr(
+      expect(function() {$rootScope.$apply(); }).toThrowMinErr(
           "$interpolate", "interr", "Can't interpolate: {{testUrl}}\nError: [$sce:insecurl] Blocked " +
           "loading resource from url not allowed by $sceDelegate policy.  URL: javascript:doTrustedStuff()");
     }));

test/ng/directive/ngSrcSpec.js

@@ -45,7 +45,7 @@ describe('ngSrc', function() {
     it('should error on non-resource_url src attributes', inject(function($compile, $rootScope, $sce) {
       element = $compile('<iframe ng-src="{{testUrl}}"></iframe>')($rootScope);
       $rootScope.testUrl = $sce.trustAsUrl("javascript:doTrustedStuff()");
-      expect($rootScope.$apply).toThrowMinErr(
+      expect(function() {$rootScope.$apply(); }).toThrowMinErr(
           "$interpolate", "interr", "Can't interpolate: {{testUrl}}\nError: [$sce:insecurl] Blocked " +
           "loading resource from url not allowed by $sceDelegate policy.  URL: " +
           "javascript:doTrustedStuff()");

test/ng/rootScopeSpec.js

@@ -72,6 +72,44 @@ describe('Scope', function() {
       expect(child.$new).toBe($rootScope.$new);
       expect(child.$root).toBe($rootScope);
     }));
+
+    it('should create a child scope with partialDigest', inject(function($rootScope, log) {
+      var child = $rootScope.$new(false, true);
+      var spyRoot = jasmine.createSpy('spyRoot');
+      var spyChild = jasmine.createSpy('spyChild');
+      $rootScope.$watch(spyRoot);
+      child.$watch(spyChild);
+
+      child.$apply();
+      expect(spyRoot).not.toHaveBeenCalled();
+      expect(spyChild).toHaveBeenCalled();
+
+      spyRoot.reset();
+      spyChild.reset();
+
+      $rootScope.$apply();
+      expect(spyRoot).toHaveBeenCalled();
+      expect(spyChild).toHaveBeenCalled();
+    }));
+
+    it('should create an isolated child scope with partialDigest', inject(function($rootScope, log) {
+      var child = $rootScope.$new(true, true);
+      var spyRoot = jasmine.createSpy('spyRoot');
+      var spyChild = jasmine.createSpy('spyChild');
+      $rootScope.$watch(spyRoot);
+      child.$watch(spyChild);
+
+      child.$apply();
+      expect(spyRoot).not.toHaveBeenCalled();
+      expect(spyChild).toHaveBeenCalled();
+
+      spyRoot.reset();
+      spyChild.reset();
+
+      $rootScope.$apply();
+      expect(spyRoot).toHaveBeenCalled();
+      expect(spyChild).toHaveBeenCalled();
+    }));
   });