Reduce leaking in object tracking tests

base/tracked_objects.cc

Index: base/tracked_objects.cc
===================================================================
--- base/tracked_objects.cc	(revision 107944)
+++ base/tracked_objects.cc	(working copy)
@@ -542,7 +542,7 @@
 }
 
 // static
-void ThreadData::ShutdownSingleThreadedCleanup() {
+void ThreadData::ShutdownSingleThreadedCleanup(bool leak) {
   // This is only called from test code, where we need to cleanup so that
   // additional tests can be run.
   // We must be single threaded... but be careful anyway.
@@ -564,12 +564,12 @@
   status_ = UNINITIALIZED;
 
   // To avoid any chance of racing in unit tests, which is the only place we
-  // call this function, we will leak all the data structures we recovered.
-  // These structures could plausibly be used by other threads in earlier tests
-  // that are still running.
-  return;
+  // call this function, we may sometimes leak all the data structures we
+  // recovered, as they may still be in use on threads from prior tests!
+  if (leak)
+    return;
 
-  // If we wanted to cleanup (on a single thread), here is what we would do.
+  // When we want to cleanup (on a single thread), here is what we do.
 
   if (final_pool) {
     // The thread_data_list contains *all* the instances, and we'll use it to