Trying changes to see the perfomance impact on Mac....

chrome/browser/browser_main.cc

Index: chrome/browser/browser_main.cc
===================================================================
--- chrome/browser/browser_main.cc	(revision 76198)
+++ chrome/browser/browser_main.cc	(working copy)
@@ -45,6 +45,7 @@
 #include "chrome/browser/metrics/histogram_synchronizer.h"
 #include "chrome/browser/metrics/metrics_log.h"
 #include "chrome/browser/metrics/metrics_service.h"
+#include "chrome/browser/metrics/thread_watcher.h"
 #include "chrome/browser/net/blob_url_request_job_factory.h"
 #include "chrome/browser/net/chrome_dns_cert_provenance_checker.h"
 #include "chrome/browser/net/chrome_dns_cert_provenance_checker_factory.h"
@@ -702,6 +703,9 @@
   process->process_launcher_thread();
   process->cache_thread();
   process->io_thread();
+  // Create watchdog thread after creating all other threads because it will
+  // watch the other threads and they must be running.
+  process->watchdog_thread();
 }
 
 // Returns the new local state object, guaranteed non-NULL.
@@ -1353,6 +1357,11 @@
   scoped_refptr<HistogramSynchronizer> histogram_synchronizer(
       new HistogramSynchronizer());
 
+  // Initialize thread watcher system. This is a singleton and is used by
+  // WatchDogThread to keep track of information about threads that are being
+  // watched.
+  scoped_ptr<ThreadWatcherList> thread_watcher_list(new ThreadWatcherList());
+
   // Initialize the prefs of the local state.
   browser::RegisterLocalState(local_state);
 
@@ -1386,6 +1395,14 @@
 
   CreateChildThreads(browser_process.get());
 
+  // Start watching all browser threads for responsiveness.
+  MessageLoop* message_loop = WatchDogThread::CurrentMessageLoop();
+  if (message_loop)
+    message_loop->PostDelayedTask(
+        FROM_HERE,
+        NewRunnableFunction(&WatchDogThread::StartWatchingAll),
+        base::TimeDelta::FromSeconds(10).InMilliseconds());
+
 #if defined(OS_CHROMEOS)
   // Now that the file thread exists we can record our stats.
   chromeos::BootTimesLoader::Get()->RecordChromeMainStats();
@@ -1903,6 +1920,9 @@
 
   process_singleton.Cleanup();
 
+  // Stop all tasks that might run on WatchDogThread.
+  ThreadWatcherList::StopWatchingAll();
+
   metrics->Stop();
 
   // browser_shutdown takes care of deleting browser_process, so we need to