[wrapper-tracing] Emite write barrier upon associating a wrapper

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

Index: third_party/WebKit/Source/bindings/core/v8/ScriptWrappable.h
diff --git a/third_party/WebKit/Source/bindings/core/v8/ScriptWrappable.h b/third_party/WebKit/Source/bindings/core/v8/ScriptWrappable.h
index 388b12d0f66b483f800f8126a314f970fa7e907e..50ba588d3011aed1d468e2b96a25cec8cebc60a0 100644
--- a/third_party/WebKit/Source/bindings/core/v8/ScriptWrappable.h
+++ b/third_party/WebKit/Source/bindings/core/v8/ScriptWrappable.h
@@ -31,6 +31,7 @@
 #ifndef ScriptWrappable_h
 #define ScriptWrappable_h
 
+#include "bindings/core/v8/ScriptWrappableVisitor.h"
 #include "bindings/core/v8/WrapperTypeInfo.h"
 #include "core/CoreExport.h"
 #include "platform/heap/Handle.h"
@@ -125,6 +126,7 @@ class CORE_EXPORT ScriptWrappable : public TraceWrapperBase {
     wrapperTypeInfo->configureWrapper(&m_mainWorldWrapper);
     m_mainWorldWrapper.SetWeak();
     ASSERT(containsWrapper());
+    ScriptWrappableVisitor::writeBarrier(this, &m_mainWorldWrapper);

[jochen (gone - plz use gerrit), 2017/03/20 20:59:39]

"this" is not necessarily pointing to the beginning of the object...

[Michael Lippautz, 2017/03/20 21:04:22]

do you have an example? I think it was the assumption that SW always has 'this'
pointing to the object start. as far as I can see we only have GarbageCollected
and GarbageCollectedFinalized in front of SW in the inheritance hierarchy. 

     return true;
   }