feat(renderer): use a comment instead of an element when stamping out template>` elements

Originally authored by @tbosch, this reverts the revert commit
e274ff8a69.

Closes #4805

modules/angular2/src/platform/dom/debug/debug_element_view_listener.ts

@@ -19,7 +19,7 @@ var _allViewsById = new Map<number, AppView>();
 var _nextId = 0;
 
 function _setElementId(element, indices: number[]) {
-  if (isPresent(element)) {
+  if (isPresent(element) && DOM.isElementNode(element)) {
     DOM.setData(element, NG_ID_PROPERTY, indices.join(NG_ID_SEPARATOR));
   }
 }

modules/angular2/test/core/linker/integration_spec.ts

@@ -476,6 +476,19 @@ export function main() {
                });
          }));
 
+      it('should use a comment while stamping out `<template>` elements.',
+         inject([TestComponentBuilder, AsyncTestCompleter], (tcb: TestComponentBuilder, async) => {
+           tcb.overrideView(MyComp, new ViewMetadata({template: '<template></template>'}))
+
+               .createAsync(MyComp)
+               .then((fixture) => {
+                 var childNodesOfWrapper = DOM.childNodes(fixture.debugElement.nativeElement);
+                 expect(childNodesOfWrapper.length).toBe(1);
+                 expect(DOM.isCommentNode(childNodesOfWrapper[0])).toBe(true);
+                 async.done();
+               });
+         }));
+
       it('should support template directives via `template` attribute.',
          inject([TestComponentBuilder, AsyncTestCompleter], (tcb: TestComponentBuilder, async) => {
            tcb.overrideView(

modules/benchmarks/e2e_test/naive_infinite_scroll_spec.ts

@@ -9,7 +9,7 @@ describe('ng2 naive infinite scroll benchmark', function() {
   it('should not throw errors', function() {
     browser.get(URL);
     var expectedRowCount = 18;
-    var expectedCellsPerRow = 28;
+    var expectedCellsPerRow = 27;
     var allScrollItems = 'scroll-app #testArea scroll-item';
     var cells = `${ allScrollItems } .row *`;
     var stageButtons = `${ allScrollItems } .row stage-buttons button`;