Adding shutdown tracing capabilities

chrome/browser/lifetime/application_lifetime.cc

Index: chrome/browser/lifetime/application_lifetime.cc
diff --git a/chrome/browser/lifetime/application_lifetime.cc b/chrome/browser/lifetime/application_lifetime.cc
index 503a0740226713866267851e18ad0b8dec5db6e2..ec209985632a3b8d87bd74cc489dcf366e7ea689 100644
--- a/chrome/browser/lifetime/application_lifetime.cc
+++ b/chrome/browser/lifetime/application_lifetime.cc
@@ -124,6 +124,16 @@ void CloseAllBrowsers() {
 }
 
 void AttemptUserExit() {
+  const CommandLine& command_line = *CommandLine::ForCurrentProcess();
+  if (command_line.HasSwitch(switches::kTraceShutdown)) {
+    base::debug::CategoryFilter category_filter(
+        command_line.GetSwitchValueASCII(switches::kTraceShutdown));
+    base::debug::TraceLog::GetInstance()->SetEnabled(
+        category_filter,
+        base::debug::TraceLog::RECORD_UNTIL_FULL);

[DaveMoore, 2013/08/30 22:51:15]

Be sure to turn off tracing if the attempt to exit fails.

[Mr4D (OOO till 08-26), 2013/08/31 02:03:44]

Good one. I haven't figured out yet how it can fail. Added a todo and will
address that later.
Note: This is a debug flag and even if the user would cancel, the buffer
capturing would stop once the buffer is full and the next time we would come
here it would start again.

Nevertheless - will ask sky about all possibilities of all OS'es since they can
vary here.

+  }
+  TRACE_EVENT0("shutdown", "AttemptUserExit");

[DaveMoore, 2013/08/30 22:51:15]

It sure would be good to get system tracing on ChromeOS too. This complicates
things quite a bit though, so it probably should come on a subsequent cl.

[Mr4D (OOO till 08-26), 2013/08/31 02:03:44]

We can add "system events" also - in a later CL as suggested.

+
 #if defined(OS_CHROMEOS)
   chromeos::BootTimesLoader::Get()->AddLogoutTimeMarker("LogoutStarted", false);
   // Write /tmp/uptime-logout-started as well.