feat(core): add ability to reflect DOM properties as attributes

By binding the token `DOM_REFLECT_PROPERTIES_AS_ATTRIBUTES` provided by 
the dom_renderer module to `true` in the root injector (i.e. bootstrap()), 
all elements whose properties are set by angular will be reflected as 
attributes with the prefix "ng-reflect-".

Fixes #2910

modules/angular2/angular2.ts

@@ -64,4 +64,8 @@ export {
   RenderViewRef,
   RenderProtoViewRef
 } from 'angular2/src/render/api';
-export {DomRenderer, DOCUMENT_TOKEN} from 'angular2/src/render/dom/dom_renderer';
+export {
+  DomRenderer,
+  DOCUMENT_TOKEN,
+  DOM_REFLECT_PROPERTIES_AS_ATTRIBUTES
+} from 'angular2/src/render/dom/dom_renderer';

modules/angular2/src/core/application.ts

@@ -56,7 +56,11 @@ import {AppViewManagerUtils} from 'angular2/src/core/compiler/view_manager_utils
 import {AppViewListener} from 'angular2/src/core/compiler/view_listener';
 import {ProtoViewFactory} from 'angular2/src/core/compiler/proto_view_factory';
 import {Renderer, RenderCompiler} from 'angular2/src/render/api';
-import {DomRenderer, DOCUMENT_TOKEN} from 'angular2/src/render/dom/dom_renderer';
+import {
+  DomRenderer,
+  DOCUMENT_TOKEN,
+  DOM_REFLECT_PROPERTIES_AS_ATTRIBUTES
+} from 'angular2/src/render/dom/dom_renderer';
 import {DefaultDomCompiler} from 'angular2/src/render/dom/compiler/compiler';
 import {internalView} from 'angular2/src/core/compiler/view_ref';
 
@@ -77,6 +81,7 @@ function _injectorBindings(appComponentType): List<Type | Binding | List<any>> {
   return [
     bind(DOCUMENT_TOKEN)
         .toValue(DOM.defaultDoc()),
+    bind(DOM_REFLECT_PROPERTIES_AS_ATTRIBUTES).toValue(false),
     bind(appComponentTypeToken).toValue(appComponentType),
     bind(appComponentRefPromiseToken)
         .toFactory(

modules/angular2/src/render/dom/dom_renderer.ts

@@ -18,19 +18,26 @@ import {DomProtoView, DomProtoViewRef, resolveInternalDomProtoView} from './view
 import {DomView, DomViewRef, resolveInternalDomView} from './view/view';
 import {DomElement} from './view/element';
 import {DomViewContainer} from './view/view_container';
-import {NG_BINDING_CLASS_SELECTOR, NG_BINDING_CLASS} from './util';
+import {NG_BINDING_CLASS_SELECTOR, NG_BINDING_CLASS, camelCaseToDashCase} from './util';
 
 import {Renderer, RenderProtoViewRef, RenderViewRef, RenderElementRef} from '../api';
 
 export const DOCUMENT_TOKEN = CONST_EXPR(new OpaqueToken('DocumentToken'));
+export const DOM_REFLECT_PROPERTIES_AS_ATTRIBUTES =
+    CONST_EXPR(new OpaqueToken('DomReflectPropertiesAsAttributes'));
+const REFLECT_PREFIX = 'ng-reflect-';
 
 @Injectable()
 export class DomRenderer extends Renderer {
   _document;
+  _reflectPropertiesAsAttributes: boolean;
 
   constructor(public _eventManager: EventManager, public _shadowDomStrategy: ShadowDomStrategy,
-              @Inject(DOCUMENT_TOKEN) document) {
+              @Inject(DOCUMENT_TOKEN) document,
+              @Inject(DOM_REFLECT_PROPERTIES_AS_ATTRIBUTES) reflectPropertiesAsAttributes:
+                  boolean) {
     super();
+    this._reflectPropertiesAsAttributes = reflectPropertiesAsAttributes;
     this._document = document;
   }
 
@@ -186,6 +193,11 @@ export class DomRenderer extends Renderer {
   setElementProperty(location: RenderElementRef, propertyName: string, propertyValue: any): void {
     var view = resolveInternalDomView(location.renderView);
     view.setElementProperty(location.boundElementIndex, propertyName, propertyValue);
+    // Reflect the property value as an attribute value with ng-reflect- prefix.
+    if (this._reflectPropertiesAsAttributes) {
+      this.setElementAttribute(location, `${REFLECT_PREFIX}${camelCaseToDashCase(propertyName)}`,
+                               propertyValue);
+    }
   }
 
   setElementAttribute(location: RenderElementRef, attributeName: string, attributeValue: string):

modules/angular2/src/test_lib/test_injector.ts

@@ -50,7 +50,11 @@ import {AppViewManagerUtils} from 'angular2/src/core/compiler/view_manager_utils
 import {ELEMENT_PROBE_CONFIG} from 'angular2/debug';
 import {ProtoViewFactory} from 'angular2/src/core/compiler/proto_view_factory';
 import {RenderCompiler, Renderer} from 'angular2/src/render/api';
-import {DomRenderer, DOCUMENT_TOKEN} from 'angular2/src/render/dom/dom_renderer';
+import {
+  DomRenderer,
+  DOCUMENT_TOKEN,
+  DOM_REFLECT_PROPERTIES_AS_ATTRIBUTES
+} from 'angular2/src/render/dom/dom_renderer';
 import {DefaultDomCompiler} from 'angular2/src/render/dom/compiler/compiler';
 
 /**
@@ -90,6 +94,7 @@ function _getAppBindings() {
         .toFactory((doc) => new EmulatedUnscopedShadowDomStrategy(doc.head), [DOCUMENT_TOKEN]),
     DomRenderer,
     DefaultDomCompiler,
+    bind(DOM_REFLECT_PROPERTIES_AS_ATTRIBUTES).toValue(false),
     bind(Renderer).toAlias(DomRenderer),
     bind(RenderCompiler).toAlias(DefaultDomCompiler),
     ProtoViewFactory,

modules/angular2/test/render/dom/dom_renderer_integration_spec.ts

@@ -19,6 +19,8 @@ import {DOM} from 'angular2/src/dom/dom_adapter';
 import {DomTestbed, TestView, elRef} from './dom_testbed';
 
 import {ViewDefinition, DirectiveMetadata, RenderViewRef} from 'angular2/src/render/api';
+import {DOM_REFLECT_PROPERTIES_AS_ATTRIBUTES} from 'angular2/src/render/dom/dom_renderer';
+import {bind} from 'angular2/di';
 
 export function main() {
   describe('DomRenderer integration', () => {
@@ -126,6 +128,50 @@ export function main() {
              });
        }));
 
+
+    it('should NOT reflect property values as attributes if flag is NOT set',
+       inject([AsyncTestCompleter, DomTestbed], (async, tb) => {
+         tb.compileAll([
+             someComponent,
+             new ViewDefinition(
+                 {componentId: 'someComponent', template: '<input [title]="y">', directives: []})
+           ])
+             .then((protoViewDtos) => {
+               var rootView = tb.createRootView(protoViewDtos[0]);
+               var cmpView = tb.createComponentView(rootView.viewRef, 0, protoViewDtos[1]);
+               var el = DOM.childNodes(tb.rootEl)[0];
+               tb.renderer.setElementProperty(elRef(cmpView.viewRef, 0), 'maxLength', '20');
+               expect(DOM.getAttribute(<HTMLInputElement>el, 'ng-reflect-max-length'))
+                   .toEqual(null);
+
+               async.done();
+             });
+       }));
+
+    describe('reflection', () => {
+      beforeEachBindings(() => [bind(DOM_REFLECT_PROPERTIES_AS_ATTRIBUTES).toValue(true)]);
+      it('should reflect property values as attributes if flag is set',
+         inject([AsyncTestCompleter, DomTestbed], (async, tb) => {
+           tb.compileAll([
+               someComponent,
+               new ViewDefinition({
+                 componentId: 'someComponent',
+                 template: '<input [title]="y">',
+                 directives: []
+               })
+             ])
+               .then((protoViewDtos) => {
+                 var rootView = tb.createRootView(protoViewDtos[0]);
+                 var cmpView = tb.createComponentView(rootView.viewRef, 0, protoViewDtos[1]);
+                 var el = DOM.childNodes(tb.rootEl)[0];
+                 tb.renderer.setElementProperty(elRef(cmpView.viewRef, 0), 'maxLength', '20');
+                 expect(DOM.getAttribute(<HTMLInputElement>el, 'ng-reflect-max-length'))
+                     .toEqual('20');
+                 async.done();
+               });
+         }));
+    });
+
     if (DOM.supportsDOMEvents()) {
       it('should call actions on the element independent of the compilation',
          inject([AsyncTestCompleter, DomTestbed], (async, tb) => {