[DevTools] Move DevToolsWindow testing code to a separate class.

chrome/browser/policy/policy_browsertest.cc

Index: chrome/browser/policy/policy_browsertest.cc
diff --git a/chrome/browser/policy/policy_browsertest.cc b/chrome/browser/policy/policy_browsertest.cc
index 91eebc1d8ba33ecf5696c8d97381ae7a19e33757..2f13d0854ec5a449ce7e1e58a7cb285b209310e3 100644
--- a/chrome/browser/policy/policy_browsertest.cc
+++ b/chrome/browser/policy/policy_browsertest.cc
@@ -31,7 +31,7 @@
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/chrome_notification_types.h"
 #include "chrome/browser/content_settings/tab_specific_content_settings.h"
-#include "chrome/browser/devtools/devtools_window.h"
+#include "chrome/browser/devtools/devtools_window_testing.h"
 #include "chrome/browser/download/download_prefs.h"
 #include "chrome/browser/extensions/api/messaging/native_message_process_host.h"
 #include "chrome/browser/extensions/crx_installer.h"
@@ -1428,7 +1428,7 @@ IN_PROC_BROWSER_TEST_F(PolicyTest, DeveloperToolsDisabled) {
   content::WindowedNotificationObserver close_observer(
       content::NOTIFICATION_WEB_CONTENTS_DESTROYED,
       content::Source<content::WebContents>(
-          devtools_window->web_contents_for_test()));
+          DevToolsWindowTesting::Get(devtools_window)->main_web_contents()));
   UpdateProviderPolicy(policies);
   // wait for devtools close
   close_observer.Wait();