Start splitting out WebUI into an implementation class and an interface that each page implements...

chrome/browser/ui/webui/chromeos/choose_mobile_network_ui.h

Index: chrome/browser/ui/webui/chromeos/choose_mobile_network_ui.h
===================================================================
--- chrome/browser/ui/webui/chromeos/choose_mobile_network_ui.h	(revision 117388)
+++ chrome/browser/ui/webui/chromeos/choose_mobile_network_ui.h	(working copy)
@@ -7,11 +7,12 @@
 #pragma once
 
 #include "content/browser/webui/web_ui.h"
+#include "content/public/browser/web_ui_controller.h"
 
 namespace chromeos {
 
 // A custom WebUI that defines datasource for choosing cellular network dialog.
-class ChooseMobileNetworkUI : public WebUI {
+class ChooseMobileNetworkUI : public WebUI, public content::WebUIController {
  public:
   explicit ChooseMobileNetworkUI(content::WebContents* contents);