LazyInstance should be thread safe by default.

The only ways we use this class require it, as multiple isolates can race
to initialize data structures. This showed up as intermittant failures on
nosnap build bots.

R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/238973004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@20794 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/lazy-instance.h

@@ -66,8 +66,8 @@
 //      LAZY_INSTANCE_INITIALIZER;
 //
 // WARNINGS:
-// - This implementation of LazyInstance is NOT THREAD-SAFE by default. See
-//   ThreadSafeInitOnceTrait declared below for that.
+// - This implementation of LazyInstance IS THREAD-SAFE by default. See
+//   SingleThreadInitOnceTrait if you don't care about thread safety.
 // - Lazy initialization comes with a cost. Make sure that you don't use it on
 //   critical path. Consider adding your initialization code to a function
 //   which is explicitly called once.
@@ -227,7 +227,7 @@ struct LazyInstanceImpl {
 
 template <typename T,
           typename CreateTrait = DefaultConstructTrait<T>,
-          typename InitOnceTrait = SingleThreadInitOnceTrait,
+          typename InitOnceTrait = ThreadSafeInitOnceTrait,
           typename DestroyTrait = LeakyInstanceTrait<T> >
 struct LazyStaticInstance {
   typedef LazyInstanceImpl<T, StaticallyAllocatedInstanceTrait<T>,
@@ -237,7 +237,7 @@ struct LazyStaticInstance {
 
 template <typename T,
           typename CreateTrait = DefaultConstructTrait<T>,
-          typename InitOnceTrait = SingleThreadInitOnceTrait,
+          typename InitOnceTrait = ThreadSafeInitOnceTrait,
           typename DestroyTrait = LeakyInstanceTrait<T> >
 struct LazyInstance {
   // A LazyInstance is a LazyStaticInstance.
@@ -248,7 +248,7 @@ struct LazyInstance {
 
 template <typename T,
           typename CreateTrait = DefaultCreateTrait<T>,
-          typename InitOnceTrait = SingleThreadInitOnceTrait,
+          typename InitOnceTrait = ThreadSafeInitOnceTrait,
           typename DestroyTrait = LeakyInstanceTrait<T> >
 struct LazyDynamicInstance {
   typedef LazyInstanceImpl<T, DynamicallyAllocatedInstanceTrait<T>,