[Turbofan] Fix a race on CallInterfaceDescriptor initialization.

src/interface-descriptors.h

Index: src/interface-descriptors.h
diff --git a/src/interface-descriptors.h b/src/interface-descriptors.h
index 3a46114f4bb249e9ac937e31b024bcf838469bcf..9091e598d91e10828df7efa634565cab5236b4ac 100644
--- a/src/interface-descriptors.h
+++ b/src/interface-descriptors.h
@@ -216,6 +216,8 @@ class CallInterfaceDescriptor {
 
   void Initialize(Isolate* isolate, CallDescriptors::Key key) {
     if (!data()->IsInitialized()) {
+      // We should only initialize descriptors on the isolate's main thread.
+      CHECK(ThreadId::Current().Equals(isolate->thread_id()));

[Michael Starzinger, 2016/07/21 16:36:47]

nit: DCHECK should do it.

[rmcilroy, 2016/07/22 09:16:32]

Yes sorry, thats what I original had then while testing on tsan release I wanted
to check it actually worked and forgot to change it back. Done.

       CallInterfaceDescriptorData* d = isolate->call_descriptor_data(key);
       DCHECK(d == data());  // d should be a modifiable pointer to data().
       InitializePlatformSpecific(d);