Track thread activities in order to diagnose hangs.

base/process/process_posix.cc

Index: base/process/process_posix.cc
diff --git a/base/process/process_posix.cc b/base/process/process_posix.cc
index ade82e5ce663be75a4bd376f060d8ad8354fc4b1..a9d745eeead1cfa6c426b4e974cbf2ede034a159 100644
--- a/base/process/process_posix.cc
+++ b/base/process/process_posix.cc
@@ -9,6 +9,7 @@
 #include <sys/resource.h>
 #include <sys/wait.h>
 
+#include "base/debug/activity_tracker.h"
 #include "base/files/scoped_file.h"
 #include "base/logging.h"
 #include "base/posix/eintr_wrapper.h"
@@ -354,6 +355,9 @@ bool Process::WaitForExit(int* exit_code) {
 }
 
 bool Process::WaitForExitWithTimeout(TimeDelta timeout, int* exit_code) {
+  // Record the event that this thread is blocking upon (for hang diagnosis).
+  base::debug::ScopedProcessWaitActivity process_activity(this);
+
   return WaitForExitWithTimeoutImpl(Handle(), exit_code, timeout);
 }