refactor(render): don’t store DOM nodes but store strings for big ProtoViews.

Also inserts comment nodes before/after projected nodes so that text nodes don’t get merged when we serialize/deserialize them.

Closes #3356
First part of #3364

modules/angular2/src/test_lib/utils.ts

@@ -77,6 +77,8 @@ export function stringifyElement(el): string {
     if (!ListWrapper.contains(_singleTagWhitelist, tagName)) {
       result += `</${tagName}>`;
     }
+  } else if (DOM.isCommentNode(el)) {
+    result += `<!--${DOM.nodeValue(el)}-->`;
   } else {
     result += DOM.getText(el);
   }