Cleanup: Pull some browser keep alive functions into its own file.

chrome/browser/ui/browser.cc

Index: chrome/browser/ui/browser.cc
diff --git a/chrome/browser/ui/browser.cc b/chrome/browser/ui/browser.cc
index 41d0a349f308eef4745faec22dd0d0a8a340a9de..3046134ccebe90e64ac68bc46d4af0a02fc697bc 100644
--- a/chrome/browser/ui/browser.cc
+++ b/chrome/browser/ui/browser.cc
@@ -62,6 +62,7 @@
 #include "chrome/browser/history/top_sites_factory.h"
 #include "chrome/browser/infobars/infobar_service.h"
 #include "chrome/browser/lifetime/application_lifetime.h"
+#include "chrome/browser/lifetime/browser_keep_alive.h"
 #include "chrome/browser/notifications/notification_ui_manager.h"
 #include "chrome/browser/pepper_broker_infobar_delegate.h"
 #include "chrome/browser/prefs/incognito_mode_prefs.h"
@@ -713,7 +714,7 @@ void Browser::OnWindowClosing() {
   // AppController on the Mac, or BackgroundContentsService for background
   // pages).
   bool should_quit_if_last_browser =
-      browser_shutdown::IsTryingToQuit() || !chrome::WillKeepAlive();
+      browser_shutdown::IsTryingToQuit() || !browser_lifetime::WillKeepAlive();
 
   if (should_quit_if_last_browser && chrome::ShouldStartShutdown(this)) {
 #if defined(OS_WIN)