Revert "feat(core): extract platforms out of core"

This reverts commit 3f4628c0b0.

modules/angular2/src/platform/browser/xhr_impl.dart

@@ -1,14 +0,0 @@
-library angular2.src.services.xhr_impl;
-
-import 'dart:async' show Future;
-import 'dart:html' show HttpRequest;
-import 'package:angular2/core.dart';
-import 'package:angular2/compiler.dart' show XHR;
-
-@Injectable()
-class XHRImpl extends XHR {
-  Future<String> get(String url) {
-    return HttpRequest.request(url).then((HttpRequest req) => req.responseText,
-        onError: (_) => new Future.error('Failed to load $url'));
-  }
-}

modules/angular2/src/platform/browser/xhr_impl.ts

@@ -1,39 +0,0 @@
-import {Promise, PromiseWrapper, PromiseCompleter} from 'angular2/src/facade/promise';
-import {isPresent} from 'angular2/src/facade/lang';
-import {XHR} from 'angular2/src/compiler/xhr';
-
-export class XHRImpl extends XHR {
-  get(url: string): Promise<string> {
-    var completer: PromiseCompleter < string >= PromiseWrapper.completer();
-    var xhr = new XMLHttpRequest();
-    xhr.open('GET', url, true);
-    xhr.responseType = 'text';
-
-    xhr.onload = function() {
-      // responseText is the old-school way of retrieving response (supported by IE8 & 9)
-      // response/responseType properties were introduced in XHR Level2 spec (supported by IE10)
-      var response = isPresent(xhr.response) ? xhr.response : xhr.responseText;
-
-      // normalize IE9 bug (http://bugs.jquery.com/ticket/1450)
-      var status = xhr.status === 1223 ? 204 : xhr.status;
-
-      // fix status code when it is 0 (0 status is undocumented).
-      // Occurs when accessing file resources or on Android 4.1 stock browser
-      // while retrieving files from application cache.
-      if (status === 0) {
-        status = response ? 200 : 0;
-      }
-
-      if (200 <= status && status <= 300) {
-        completer.resolve(response);
-      } else {
-        completer.reject(`Failed to load ${url}`, null);
-      }
-    };
-
-    xhr.onerror = function() { completer.reject(`Failed to load ${url}`, null); };
-
-    xhr.send();
-    return completer.promise;
-  }
-}