Fix issues with browser focus assignment (fixes issue #3306, fixes issue #3116, see issue #3040)

DesktopWindowTreeHostWin ("Chrome_WidgetWin_0") focus needs to be set
synchronously in response to the parent window WM_SETFOCUS message and
before the associated call to WebContents::Focus. See updated comments in
CefBrowserPlatformDelegateNativeWin::SetFocus.

libcef/browser/browser_host_base.h

@@ -337,8 +337,6 @@ class CefBrowserHostBase : public CefBrowserHost,
   // Called from LoadMainFrameURL to perform the actual navigation.
   virtual bool Navigate(const content::OpenURLParams& params);
 
-  void SetFocusInternal(bool focus);
-
   // Create the CefFileDialogManager if it doesn't already exist.
   bool EnsureFileDialogManager();