Set process phases in the StackSamplingProfiler.

content/public/browser/browser_main_parts.h

Index: content/public/browser/browser_main_parts.h
diff --git a/content/public/browser/browser_main_parts.h b/content/public/browser/browser_main_parts.h
index 8b41253e0574dda3bba78cbea10c0dd9af315a70..918fc8b182ce7b43bd82d70ee43a33df67fabef4 100644
--- a/content/public/browser/browser_main_parts.h
+++ b/content/public/browser/browser_main_parts.h
@@ -88,6 +88,9 @@ class CONTENT_EXPORT BrowserMainParts {
   // threads are stopped.
   virtual void PostMainMessageLoopRun() {}
 
+  // Called when shutdown is about to begin.
+  virtual void PreShutdown() {}
+
   // Called as the very last part of shutdown, after threads have been
   // stopped and destroyed.
   virtual void PostDestroyThreads() {}