Add support for HTTP handlers that are in self-contained apps. Also add an example app.

examples/http_handler/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-shared_library("wget") {
-  deps = [
-    "//mojo/public/c/system:for_shared_library",
-    "//mojo/public/cpp/application:standalone",
-    "//mojo/public/cpp/bindings",
-    "//mojo/public/cpp/utility",
-    "//mojo/services/public/interfaces/network",
+shared_library("http_handler") {
+  sources = [
+    "http_handler.cc"
   ]
 
-  sources = [
-    "wget.cc"
+  deps = [
+    "//mojo/application",
+    "//mojo/public/c/system:for_shared_library",
+    "//mojo/public/cpp/bindings",
+    "//services/http_server",
+    "//services/http_server/public",
   ]
 }