Remove redundant fetch functions and avoid crashing when no headers are set

examples/stocks/lib/stock_data.dart

@@ -10,7 +10,7 @@
 import 'dart:convert';
 import 'dart:math' as math;
 
-import 'package:flutter/services.dart';
+import 'package:flutter/http.dart' as http;
 
 final math.Random _rng = new math.Random();
 
@@ -83,8 +83,8 @@ class StockDataFetcher {
     if (!actuallyFetchData)
       return;
 
-    fetchBody(_urlToFetch(_nextChunk++)).then((Response response) {
-      String json = response.bodyAsString();
+    http.get(_urlToFetch(_nextChunk++)).then((http.Response response) {
+      String json = response.body;
       if (json == null) {
         print("Failed to load stock data chunk ${_nextChunk - 1}");
         return;

packages/flutter/lib/src/http/mojo_client.dart

@@ -66,7 +66,7 @@ class MojoClient {
       Map<String, String> headers, [body, Encoding encoding]) async {
     mojo.UrlLoaderProxy loader = new mojo.UrlLoaderProxy.unbound();
     List<mojo.HttpHeader> mojoHeaders = <mojo.HttpHeader>[];
-    headers.forEach((String name, String value) {
+    headers?.forEach((String name, String value) {
       mojo.HttpHeader header = new mojo.HttpHeader()
         ..name = name
         ..value = value;

packages/flutter/lib/src/services/asset_bundle.dart

@@ -7,6 +7,8 @@ import 'dart:ui' as ui;
 import 'dart:ui_internals' as internals;
 import 'dart:typed_data';
 
+import 'package:flutter/http.dart' as http;
+
 import 'package:mojo/core.dart' as core;
 import 'package:mojo_services/mojo/asset_bundle/asset_bundle.mojom.dart';
 
@@ -38,7 +40,7 @@ class NetworkAssetBundle extends AssetBundle {
 
   ImageResource loadImage(String key) => imageCache.load(_urlFromKey(key));
 
-  Future<String> loadString(String key) => fetchString(_urlFromKey(key));
+  Future<String> loadString(String key) => http.get(_urlFromKey(key));
 }
 
 Future _fetchAndUnpackBundle(String relativeUrl, AssetBundleProxy bundle) async {

packages/flutter/lib/src/services/fetch.dart

@@ -23,18 +23,6 @@ NetworkServiceProxy _initNetworkService() {
 
 final NetworkServiceProxy _networkService = _initNetworkService();
 
-class Response {
-  ByteData body;
-
-  Response(this.body);
-
-  String bodyAsString() {
-    if (body == null)
-      return null;
-    return new String.fromCharCodes(new Uint8List.view(body.buffer));
-  }
-}
-
 Future<UrlResponse> fetch(UrlRequest request) async {
   UrlLoaderProxy loader = new UrlLoaderProxy.unbound();
   try {
@@ -56,16 +44,3 @@ Future<UrlResponse> fetchUrl(String relativeUrl) {
     ..autoFollowRedirects = true;
   return fetch(request);
 }
-
-Future<Response> fetchBody(String relativeUrl) async {
-  UrlResponse response = await fetchUrl(relativeUrl);
-  if (response.body == null) return new Response(null);
-
-  ByteData data = await core.DataPipeDrainer.drainHandle(response.body);
-  return new Response(data);
-}
-
-Future<String> fetchString(String relativeUrl) async {
-  Response response = await fetchBody(relativeUrl);
-  return response.bodyAsString();
-}

packages/updater/lib/main.dart

@@ -6,6 +6,7 @@ import 'dart:async';
 import 'dart:io';
 
 import 'package:mojo/core.dart';
+import 'package:flutter/http.dart' as http;
 import 'package:flutter/services.dart';
 import 'package:flx/bundle.dart';
 import 'package:sky_services/updater/update_service.mojom.dart';
@@ -82,7 +83,7 @@ class UpdateTask {
 
   Future<yaml.YamlMap> _fetchManifest() async {
     String manifestUrl = _currentManifest['update-url'] + '/' + kManifestFile;
-    String manifestData = await fetchString(manifestUrl);
+    String manifestData = await http.get(manifestUrl);
     return yaml.loadYaml(manifestData, sourceUrl: manifestUrl);
   }