Removes the dependency to WMTestHelper from app shell.

apps/shell/browser/shell_browser_main_parts.h

Index: apps/shell/browser/shell_browser_main_parts.h
diff --git a/apps/shell/browser/shell_browser_main_parts.h b/apps/shell/browser/shell_browser_main_parts.h
index d8a2c118f5b9567d80a5ec2539db7172043a9b50..e9e149175205756ddbd99cb634c9fb09ff302c64 100644
--- a/apps/shell/browser/shell_browser_main_parts.h
+++ b/apps/shell/browser/shell_browser_main_parts.h
@@ -43,8 +43,7 @@ class ShellNetworkController;
 #endif
 
 // Handles initialization of AppShell.
-class ShellBrowserMainParts : public content::BrowserMainParts,
-                              public aura::WindowTreeHostObserver {
+class ShellBrowserMainParts : public content::BrowserMainParts {
  public:
   ShellBrowserMainParts(const content::MainFunctionParams& parameters,
                         ShellBrowserMainDelegate* browser_main_delegate);
@@ -68,9 +67,6 @@ class ShellBrowserMainParts : public content::BrowserMainParts,
   virtual void PostMainMessageLoopRun() OVERRIDE;
   virtual void PostDestroyThreads() OVERRIDE;
 
-  // aura::WindowTreeHostObserver overrides:
-  virtual void OnHostCloseRequested(const aura::WindowTreeHost* host) OVERRIDE;
-
  private:
   // Creates and initializes the ExtensionSystem.
   void CreateExtensionSystem();