Introduce chrome.shell.createWindow stub API for app_shell

chrome/renderer/chrome_content_renderer_client.cc

Index: chrome/renderer/chrome_content_renderer_client.cc
diff --git a/chrome/renderer/chrome_content_renderer_client.cc b/chrome/renderer/chrome_content_renderer_client.cc
index 7101411854cac8efa6edc0dc8410dacfa847754b..20c9d6bf5537e5fb86dbdf07145d27866768bae8 100644
--- a/chrome/renderer/chrome_content_renderer_client.cc
+++ b/chrome/renderer/chrome_content_renderer_client.cc
@@ -236,6 +236,13 @@ void ChromeContentRendererClient::RenderThreadStarted() {
   RenderThread* thread = RenderThread::Get();
 
   chrome_observer_.reset(new ChromeRenderProcessObserver(this));
+
+  // Extensions clients must be created before extensions::Dispatcher.
+  extensions::ExtensionsClient::Set(
+      extensions::ChromeExtensionsClient::GetInstance());
+  extensions::ExtensionsRendererClient::Set(
+      ChromeExtensionsRendererClient::GetInstance());
+
   // ChromeRenderViewTest::SetUp() creates its own ExtensionDispatcher and
   // injects it using SetExtensionDispatcher(). Don't overwrite it.
   if (!extension_dispatcher_)
@@ -359,11 +366,6 @@ void ChromeContentRendererClient::RenderThreadStarted() {
   WebSecurityPolicy::registerURLSchemeAsBypassingContentSecurityPolicy(
       extension_resource_scheme);
 
-  extensions::ExtensionsClient::Set(
-      extensions::ChromeExtensionsClient::GetInstance());
-  extensions::ExtensionsRendererClient::Set(
-      ChromeExtensionsRendererClient::GetInstance());
-
 #if defined(OS_WIN)
   // Report if the renderer process has been patched by chrome_elf.
   // TODO(csharp): Remove once the renderer is no longer getting