Upstream the iOS web_shell and supporting code

ios/web/shell/shell_web_main_parts.mm

Index: ios/web/shell/shell_web_main_parts.mm
diff --git a/ios/web/shell/shell_web_main_parts.mm b/ios/web/shell/shell_web_main_parts.mm
new file mode 100644
index 0000000000000000000000000000000000000000..1a1c7eeb1a29d467c2481106d46a7cab921dbf86
--- /dev/null
+++ b/ios/web/shell/shell_web_main_parts.mm
@@ -0,0 +1,21 @@
+// 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.
+
+#include "ios/web/shell/shell_web_main_parts.h"
+
+#include "ios/web/shell/shell_browser_state.h"
+
+namespace web {
+
+ShellWebMainParts::ShellWebMainParts() {
+}
+
+ShellWebMainParts::~ShellWebMainParts() {
+}
+
+void ShellWebMainParts::PreMainMessageLoopRun() {
+  browser_state_.reset(new ShellBrowserState);
+}
+
+}  // namespace web