Track thread activities in order to diagnose hangs.

base/threading/platform_thread_win.cc

Index: base/threading/platform_thread_win.cc
diff --git a/base/threading/platform_thread_win.cc b/base/threading/platform_thread_win.cc
index 230178d646bf61543235560486fcda4cc7e42c6f..117f36c83e6db1d852131e1d09dd4e929f08afd8 100644
--- a/base/threading/platform_thread_win.cc
+++ b/base/threading/platform_thread_win.cc
@@ -6,6 +6,7 @@
 
 #include <stddef.h>
 
+#include "base/debug/activity_tracker.h"
 #include "base/debug/alias.h"
 #include "base/debug/profiler.h"
 #include "base/logging.h"
@@ -202,6 +203,9 @@ bool PlatformThread::CreateNonJoinable(size_t stack_size, Delegate* delegate) {
 
 // static
 void PlatformThread::Join(PlatformThreadHandle thread_handle) {
+  // Record the event that this thread is blocking upon (for hang diagnosis).
+  base::debug::ScopedThreadJoinActivity thread_activity(&thread_handle);
+
   DCHECK(thread_handle.platform_handle());
   // TODO(willchan): Enable this check once I can get it to work for Windows
   // shutdown.