For a worker, mark relative to its wrapper map.

third_party/WebKit/Source/bindings/core/v8/DOMWrapperWorld.cpp

Index: third_party/WebKit/Source/bindings/core/v8/DOMWrapperWorld.cpp
diff --git a/third_party/WebKit/Source/bindings/core/v8/DOMWrapperWorld.cpp b/third_party/WebKit/Source/bindings/core/v8/DOMWrapperWorld.cpp
index 9e6672465511eb4ba8ab3d079ed680d821684127..b09e47092f972643333fb67394f18d3cc0f46c5d 100644
--- a/third_party/WebKit/Source/bindings/core/v8/DOMWrapperWorld.cpp
+++ b/third_party/WebKit/Source/bindings/core/v8/DOMWrapperWorld.cpp
@@ -133,10 +133,19 @@ void DOMWrapperWorld::markWrappersInAllWorlds(
   // needed (there is no way to get from one wrapper to another), nor wanted
   // (big performance and memory overhead).
 
-  // Marking for the main world
-  scriptWrappable->markWrapper(visitor);
-  if (!isMainThread())
+  // Handle marking in per-worker wrapper worlds.
+  if (!isMainThread()) {
+    v8::Isolate* isolate = ThreadState::current()->isolate();
+    if (isolate && !isolate->GetCurrentContext().IsEmpty()) {

[jochen (gone - plz use gerrit), 2017/01/30 15:34:01]

maybe remove the GetCurrentContext() call? That creates handles, but we're not
necessarily in a handlescope here (and gc creating handles isn't that great
either)

+      DOMDataStore& dataStore =
+          DOMWrapperWorld::current(isolate).domDataStore();
+      if (dataStore.containsWrapper(scriptWrappable)) {
+        dataStore.markWrapper(scriptWrappable);
+      }
+    }
     return;
+  }
+  scriptWrappable->markWrapper(visitor);
   WorldMap& isolatedWorlds = isolatedWorldMap();
   for (auto& world : isolatedWorlds.values()) {
     DOMDataStore& dataStore = world->domDataStore();