WTF: Initialize main-thread stack estimates when WTF starts up.

third_party/WebKit/Source/wtf/Threading.h

Index: third_party/WebKit/Source/wtf/Threading.h
diff --git a/third_party/WebKit/Source/wtf/Threading.h b/third_party/WebKit/Source/wtf/Threading.h
index 784470c708f8127ea9ce008e5513abf44b03d130..4f01de86684482ca0e56f524ac18fa25ef1e8d14 100644
--- a/third_party/WebKit/Source/wtf/Threading.h
+++ b/third_party/WebKit/Source/wtf/Threading.h
@@ -47,6 +47,9 @@ namespace internal {
 WTF_EXPORT ThreadIdentifier currentThreadSyscall();
 }  // namespace internal
 
+// Must be called before |currentThread|.

[haraken, 2017/03/06 01:44:03]

Can we add a dcheck about this fact?

BTW, who calls initializeCurrentThread on non-main threads?

[jbroman, 2017/03/06 16:14:03]

Sure.
Nobody. This just does the one-time initialization needed: a pthread_key_t (or
its Windows equivalent) needs to be created before thread-local lookups can be
done, so it just needs to be done on some thread once before currentThread is
called. currentThread could do this internally (and create the key on first use,
assuming that it will be before a thread race exists), but this seems clearer
and has fewer branches in the hot path.

+WTF_EXPORT void initializeCurrentThread();
+
 WTF_EXPORT ThreadIdentifier currentThread();
 
 #if DCHECK_IS_ON()