Assert on deleting a held lock.

base/synchronization/lock.cc

Index: base/synchronization/lock.cc
diff --git a/base/synchronization/lock.cc b/base/synchronization/lock.cc
index 6445ce8a853d591bb3a8a2aca63ef0fa2f6b796b..49efbe926517342f079959386c2103295ddda0f9 100644
--- a/base/synchronization/lock.cc
+++ b/base/synchronization/lock.cc
@@ -13,9 +13,16 @@
 
 namespace base {
 
+const PlatformThreadId kNoThreadId = static_cast<PlatformThreadId>(0);
+
 Lock::Lock() : lock_() {
   owned_by_thread_ = false;
-  owning_thread_id_ = static_cast<PlatformThreadId>(0);
+  owning_thread_id_ = kNoThreadId;
+}
+
+Lock::~Lock() {
+  DCHECK(!owned_by_thread_);
+  DCHECK_EQ(kNoThreadId, owning_thread_id_);
 }
 
 void Lock::AssertAcquired() const {
@@ -27,7 +34,7 @@ void Lock::CheckHeldAndUnmark() {
   DCHECK(owned_by_thread_);
   DCHECK_EQ(owning_thread_id_, PlatformThread::CurrentId());
   owned_by_thread_ = false;
-  owning_thread_id_ = static_cast<PlatformThreadId>(0);
+  owning_thread_id_ = kNoThreadId;
 }
 
 void Lock::CheckUnheldAndMark() {