Removes the dependency to WMTestHelper from app shell.

apps/shell/browser/shell_browser_main_parts.cc

Index: apps/shell/browser/shell_browser_main_parts.cc
diff --git a/apps/shell/browser/shell_browser_main_parts.cc b/apps/shell/browser/shell_browser_main_parts.cc
index b409f1775c301e8401a440f69483a8c107c9a79f..625ccf89ee2f7a68b71a2e23bc76b9d7740145af 100644
--- a/apps/shell/browser/shell_browser_main_parts.cc
+++ b/apps/shell/browser/shell_browser_main_parts.cc
@@ -81,8 +81,9 @@ void ShellBrowserMainParts::PreMainMessageLoopRun() {
   // Initialize our "profile" equivalent.
   browser_context_.reset(new ShellBrowserContext);
 
-  desktop_controller_.reset(new ShellDesktopController);
-  desktop_controller_->GetWindowTreeHost()->AddObserver(this);
+  desktop_controller_.reset(browser_main_delegate_->CreateDesktopController());
+  desktop_controller_->CreateRootWindow();
+  desktop_controller_->host()->AddObserver(this);
 
   // NOTE: Much of this is culled from chrome/test/base/chrome_test_suite.cc
   // TODO(jamescook): Initialize chromeos::UserManager.
@@ -136,7 +137,7 @@ void ShellBrowserMainParts::PostMainMessageLoopRun() {
   extensions_browser_client_.reset();
   browser_context_.reset();
 
-  desktop_controller_->GetWindowTreeHost()->RemoveObserver(this);
+  desktop_controller_->host()->RemoveObserver(this);
   desktop_controller_.reset();
 }