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

chrome/browser/metro_viewer/chrome_metro_viewer_process_host_aurawin.cc

Index: chrome/browser/metro_viewer/chrome_metro_viewer_process_host_aurawin.cc
diff --git a/chrome/browser/metro_viewer/chrome_metro_viewer_process_host_aurawin.cc b/chrome/browser/metro_viewer/chrome_metro_viewer_process_host_aurawin.cc
index 4b3f4a65773213c4a6b77d2ff5c5a540455e52b5..2aa2e9475cd8acb9ecb196d09e07068fa3a92077 100644
--- a/chrome/browser/metro_viewer/chrome_metro_viewer_process_host_aurawin.cc
+++ b/chrome/browser/metro_viewer/chrome_metro_viewer_process_host_aurawin.cc
@@ -17,6 +17,7 @@
 #include "chrome/browser/browser_shutdown.h"
 #include "chrome/browser/chrome_notification_types.h"
 #include "chrome/browser/lifetime/application_lifetime.h"
+#include "chrome/browser/lifetime/browser_keep_alive.h"
 #include "chrome/browser/profiles/profile_manager.h"
 #include "chrome/browser/search_engines/template_url_service_factory.h"
 #include "chrome/browser/ui/ash/ash_init.h"
@@ -73,10 +74,11 @@ ChromeMetroViewerProcessHost::ChromeMetroViewerProcessHost()
     : MetroViewerProcessHost(
           content::BrowserThread::GetMessageLoopProxyForThread(
               content::BrowserThread::IO)) {
-  chrome::IncrementKeepAliveCount();
+  keep_alive_.reset(new browser_lifetime::ScopedKeepAlive);
 }
 
 ChromeMetroViewerProcessHost::~ChromeMetroViewerProcessHost() {
+  DCHECK(!keep_alive_);
 }
 
 void ChromeMetroViewerProcessHost::OnChannelError() {
@@ -93,7 +95,7 @@ void ChromeMetroViewerProcessHost::OnChannelError() {
   if (aura::RemoteWindowTreeHostWin::Instance()) {
     aura::RemoteWindowTreeHostWin::Instance()->Disconnected();
 
-    chrome::DecrementKeepAliveCount();
+    keep_alive_.reset();
 
     // If browser is trying to quit, we shouldn't reenter the process.
     // TODO(shrikant): In general there seem to be issues with how AttemptExit
@@ -110,7 +112,7 @@ void ChromeMetroViewerProcessHost::OnChannelError() {
     return;
   }
 
-  chrome::DecrementKeepAliveCount();
+  keep_alive_.reset();
 
   // This will delete the MetroViewerProcessHost object. Don't access member
   // variables/functions after this call.