Tidy DEFINE_(THREAD_SAFE_)STATIC_LOCAL() implementations.

third_party/WebKit/Source/bindings/core/v8/ScriptWrappable.h

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 43 matching lines @@
 // ScriptWrappable provides a way to map from/to C++ DOM implementation to/from
 // JavaScript object (platform object).  ToV8() converts a ScriptWrappable to
 // a v8::Object and toScriptWrappable() converts a v8::Object back to
 // a ScriptWrappable.  v8::Object as platform object is called "wrapper object".
 // The wrapepr object for the main world is stored in ScriptWrappable.  Wrapper
 // objects for other worlds are stored in DOMWrapperMap.
 class CORE_EXPORT ScriptWrappable : public TraceWrapperBase {
   WTF_MAKE_NONCOPYABLE(ScriptWrappable);
 
  public:
-  ScriptWrappable() {}
+  ScriptWrappable() {
+#if DCHECK_IS_ON()
+    // If this DCHECK() triggers, you're attempting to embed a ScriptWrappable
+    // inside a static local singleton, which is unsafe.
+    // See |DEFINE_STATIC_LOCAL()| documentation for further details.
+    DCHECK(ThreadState::current()->canAllocateScriptWrappable());
+#endif
+  }
 
   bool isScriptWrappable() const override { return true; }
 
   template <typename T>
   T* toImpl() {
     // All ScriptWrappables are managed by the Blink GC heap; check that
     // |T| is a garbage collected type.
     static_assert(
         sizeof(T) && WTF::IsGarbageCollectedType<T>::value,
         "Classes implementing ScriptWrappable must be garbage collected.");
@@ skipping 144 matching lines @@
 #define DECLARE_WRAPPERTYPEINFO()                          \
  public:                                                   \
   const WrapperTypeInfo* wrapperTypeInfo() const override; \
                                                            \
  private:                                                  \
   typedef void end_of_define_wrappertypeinfo_not_reached_t
 
 }  // namespace blink
 
 #endif  // ScriptWrappable_h