refactor(render): add DomElement

Replaces the multiple arrays of `DomView`
by a single array with `DomElement`s.

Note: this commit does not show a performance regression
(tested against the tree benchmark locally).

modules/angular2/src/debug/debug_element.ts

@@ -43,7 +43,9 @@ export class DebugElement {
   }
 
   get domElement(): any {
-    return resolveInternalDomView(this._parentView.render).boundElements[this._boundElementIndex];
+    return resolveInternalDomView(this._parentView.render)
+        .boundElements[this._boundElementIndex]
+        .element;
   }
 
   getDirectiveInstance(directiveIndex: number): any {