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

chrome/browser/app_controller_mac.mm

Index: chrome/browser/app_controller_mac.mm
diff --git a/chrome/browser/app_controller_mac.mm b/chrome/browser/app_controller_mac.mm
index 708f81e0a6f92e0706fe9ebb819bae888ab70354..f3267d21c68a52403441116c562fbe00373b49eb 100644
--- a/chrome/browser/app_controller_mac.mm
+++ b/chrome/browser/app_controller_mac.mm
@@ -32,6 +32,7 @@
 #include "chrome/browser/extensions/extension_service.h"
 #include "chrome/browser/first_run/first_run.h"
 #include "chrome/browser/lifetime/application_lifetime.h"
+#include "chrome/browser/lifetime/browser_keep_alive.h"
 #include "chrome/browser/mac/mac_startup_profiler.h"
 #include "chrome/browser/prefs/incognito_mode_prefs.h"
 #include "chrome/browser/profiles/profile_info_cache_observer.h"
@@ -518,7 +519,7 @@ class AppControllerProfileObserver : public ProfileInfoCacheObserver {
 
   // Tell BrowserList not to keep the browser process alive. Once all the
   // browsers get dealloc'd, it will stop the RunLoop and fall back into main().
-  chrome::DecrementKeepAliveCount();
+  keep_alive_.reset();
 
   // Reset all pref watching, as this object outlives the prefs system.
   profilePrefRegistrar_.reset();
@@ -730,7 +731,7 @@ class AppControllerProfileObserver : public ProfileInfoCacheObserver {
 
   // Notify BrowserList to keep the application running so it doesn't go away
   // when all the browser windows get closed.
-  chrome::IncrementKeepAliveCount();
+  keep_alive_.reset(new browser_lifetime::ScopedKeepAlive);
 
   [self setUpdateCheckInterval];