Temporary instrumentation to help understand lock errors on mac debug bots.

base/synchronization/lock_impl_posix.cc

Index: base/synchronization/lock_impl_posix.cc
===================================================================
--- base/synchronization/lock_impl_posix.cc	(revision 107048)
+++ base/synchronization/lock_impl_posix.cc	(working copy)
@@ -12,6 +12,10 @@
 namespace internal {
 
 LockImpl::LockImpl() {
+#ifdef LOCK_IMPL_CHECK_LIVENESS
+  liveness_token_ = LT_ALIVE;
+#endif
+
 #ifndef NDEBUG
   // In debug, setup attributes for lock error checking.
   pthread_mutexattr_t mta;
@@ -30,25 +34,45 @@
 }
 
 LockImpl::~LockImpl() {
+#ifdef LOCK_IMPL_CHECK_LIVENESS
+  CheckIsAlive();
+  liveness_token_ = LT_DELETED;
+#endif
   int rv = pthread_mutex_destroy(&os_lock_);
   DCHECK_EQ(rv, 0);
 }
 
 bool LockImpl::Try() {
+#ifdef LOCK_IMPL_CHECK_LIVENESS
+  CheckIsAlive();
+#endif
   int rv = pthread_mutex_trylock(&os_lock_);
   DCHECK(rv == 0 || rv == EBUSY);
   return rv == 0;
 }
 
 void LockImpl::Lock() {
+#ifdef LOCK_IMPL_CHECK_LIVENESS
+  CheckIsAlive();
+#endif
   int rv = pthread_mutex_lock(&os_lock_);
   DCHECK_EQ(rv, 0);
 }
 
 void LockImpl::Unlock() {
+#ifdef LOCK_IMPL_CHECK_LIVENESS
+  CheckIsAlive();
+#endif
   int rv = pthread_mutex_unlock(&os_lock_);
   DCHECK_EQ(rv, 0);
 }
 
+#ifdef LOCK_IMPL_CHECK_LIVENESS
+void LockImpl::CheckIsAlive() {
+  CHECK_EQ(LT_ALIVE, liveness_token_)
+      << "Lock was invalid. Please see: http://crbug.com/102161";
+}
+#endif
+
 }  // namespace internal
 }  // namespace base