feat(debug): replace DebugElement with new Debug DOM

Now, using `ng.probe(element)` in the browser console returns
a DebugElement when in dev mode.

`ComponentFixture#debugElement` also returns a new DebugElement.

Breaking Change:

This is a breaking change for unit tests. The API for the DebugElement
has changed. Now, there is a DebugElement or DebugNode for every node
in the DOM, not only nodes with an ElementRef. `componentViewChildren` is
removed, and `childNodes` is a list of ElementNodes corresponding to every
child in the DOM. `query` no longer takes a scope parameter, since
the entire rendered DOM is included in the `childNodes`.

Before:

```
componentFixture.debugElement.componentViewChildren[0];
```

After
```
// Depending on the DOM structure of your component, the
// index may have changed or the first component child
// may be a sub-child.
componentFixture.debugElement.children[0];
```

Before:

```
debugElement.query(By.css('div'), Scope.all());
```

After:

```
debugElement.query(By.css('div'));
```

Before:

```
componentFixture.debugElement.elementRef;
```

After:

```
componentFixture.elementRef;
```

modules/angular2/src/testing/test_component_builder.ts

@@ -1,11 +1,11 @@
 import {
   ComponentRef,
-  DebugElement,
   DirectiveResolver,
   DynamicComponentLoader,
   Injector,
   Injectable,
   ViewMetadata,
+  ElementRef,
   EmbeddedViewRef,
   ViewResolver,
   provide
@@ -23,7 +23,7 @@ import {el} from './utils';
 import {DOCUMENT} from 'angular2/src/platform/dom/dom_tokens';
 import {DOM} from 'angular2/src/platform/dom/dom_adapter';
 
-import {DebugElement_} from 'angular2/src/core/debug/debug_element';
+import {DebugNode, DebugElement, getDebugNode} from 'angular2/src/core/debug/debug_node';
 
 
 /**
@@ -45,6 +45,11 @@ export abstract class ComponentFixture {
    */
   nativeElement: any;
 
+  /**
+   * The ElementRef for the element at the root of the component.
+   */
+  elementRef: ElementRef;
+
   /**
    * Trigger a change detection cycle for the component.
    */
@@ -66,7 +71,9 @@ export class ComponentFixture_ extends ComponentFixture {
   constructor(componentRef: ComponentRef) {
     super();
     this._componentParentView = (<ViewRef_>componentRef.hostView).internalView;
-    this.debugElement = new DebugElement_(this._componentParentView.appElements[0]);
+    this.elementRef = this._componentParentView.appElements[0].ref;
+    this.debugElement = <DebugElement>getDebugNode(
+        this._componentParentView.rootNodesOrAppElements[0].nativeElement);
     this.componentInstance = this.debugElement.componentInstance;
     this.nativeElement = this.debugElement.nativeElement;
     this._componentRef = componentRef;