Instrument some of the exit paths likely to suffer hangs.

chrome/browser/ui/views/frame/browser_desktop_window_tree_host_win.cc

Index: chrome/browser/ui/views/frame/browser_desktop_window_tree_host_win.cc
diff --git a/chrome/browser/ui/views/frame/browser_desktop_window_tree_host_win.cc b/chrome/browser/ui/views/frame/browser_desktop_window_tree_host_win.cc
index 16dc6e592200835c4a253181a66a670c5ca46964..a2802990a93098d8a1fc4e876b0866e830eba055 100644
--- a/chrome/browser/ui/views/frame/browser_desktop_window_tree_host_win.cc
+++ b/chrome/browser/ui/views/frame/browser_desktop_window_tree_host_win.cc
@@ -6,6 +6,7 @@
 
 #include <dwmapi.h>
 
+#include "base/process/process_handle.h"
 #include "chrome/browser/lifetime/application_lifetime.h"
 #include "chrome/browser/themes/theme_service.h"
 #include "chrome/browser/themes/theme_service_factory.h"
@@ -16,6 +17,8 @@
 #include "chrome/browser/ui/views/frame/system_menu_insertion_delegate_win.h"
 #include "chrome/browser/ui/views/tabs/tab_strip.h"
 #include "chrome/browser/ui/views/theme_image_mapper.h"
+#include "chrome/common/chrome_constants.h"
+#include "components/browser_watcher/exit_funnel_win.h"
 #include "ui/base/theme_provider.h"
 #include "ui/gfx/win/dpi.h"
 #include "ui/views/controls/menu/native_menu_win.h"
@@ -70,6 +73,31 @@ class DesktopThemeProvider : public ui::ThemeProvider {
   DISALLOW_COPY_AND_ASSIGN(DesktopThemeProvider);
 };
 
+// See http://crbug.com/412384.
+void TraceSessionEnding(LPARAM lparam) {
+  browser_watcher::ExitFunnel funnel;
+  if (!funnel.Init(chrome::kBrowserExitCodesRegistryPath,
+                   base::GetCurrentProcessHandle())) {
+    return;
+  }
+
+  // This exit path is the prime suspect for most our unclean shutdowns.
+  // Trace all the possible options to WM_ENDSESSION. This may result in
+  // multiple events for a single shutdown, but that's fine.
+  funnel.RecordEvent(L"WM_ENDSESSION");
+
+  if (lparam & ENDSESSION_CLOSEAPP)
+    funnel.RecordEvent(L"ES_CloseApp");
+  if (lparam & ENDSESSION_CRITICAL)
+    funnel.RecordEvent(L"ES_Critical");
+  if (lparam & ENDSESSION_LOGOFF)
+    funnel.RecordEvent(L"ES_Logoff");
+  const LPARAM kKnownBits =
+      ENDSESSION_CLOSEAPP | ENDSESSION_CRITICAL | ENDSESSION_LOGOFF;
+  if (lparam & ~kKnownBits)
+    funnel.RecordEvent(L"ES_Other");
+}
+
 }  // namespace
 
 ////////////////////////////////////////////////////////////////////////////////
@@ -182,6 +210,7 @@ bool BrowserDesktopWindowTreeHostWin::PreHandleMSG(UINT message,
         minimize_button_metrics_.OnHWNDActivated();
       return false;
     case WM_ENDSESSION:
+      TraceSessionEnding(l_param);
       chrome::SessionEnding();
       return true;
     case WM_INITMENUPOPUP: