Add a thread-safety assertion in DEFINE_STATIC_LOCAL

Source/platform/WebThreadSupportingGC.cpp

Index: Source/platform/WebThreadSupportingGC.cpp
diff --git a/Source/platform/WebThreadSupportingGC.cpp b/Source/platform/WebThreadSupportingGC.cpp
index df76335a69473b83aed6c4e6dd002bd3b9652250..b08ed0e27448628b6844e04dcc8f5578f52a8c16 100644
--- a/Source/platform/WebThreadSupportingGC.cpp
+++ b/Source/platform/WebThreadSupportingGC.cpp
@@ -5,10 +5,15 @@
 #include "config.h"
 #include "platform/WebThreadSupportingGC.h"
 
+#include "wtf/Threading.h"
+
 namespace blink {
 
 PassOwnPtr<WebThreadSupportingGC> WebThreadSupportingGC::create(const char* name)
 {
+#if ENABLE(ASSERT)
+    WTF::willCreateThread();

[kbalazs, 2015/02/11 05:08:47]

How will people not forget to do this when they happen to add a new thread? Can
it be part of creation of WebThread?

Btw imho it would be nicer to #if guard the body of the function.

[kinuko, 2015/02/12 02:31:22]

I assumed that in blink we'll be anyway using WebThreadSupportingGC in most
cases, if not all.
Yup, might be. Feel free to create a patch :)

+#endif
     return adoptPtr(new WebThreadSupportingGC(name));
 }