Oilpan: move WorkerGlobalScope to oilpan's heap.

Source/core/workers/WorkerThread.cpp

Index: Source/core/workers/WorkerThread.cpp
diff --git a/Source/core/workers/WorkerThread.cpp b/Source/core/workers/WorkerThread.cpp
index b59b7f0226eb85b053dff42599223be1825152c8..8c77e0b1e9ba66d08cf645532c5f9c7f5198da69 100644
--- a/Source/core/workers/WorkerThread.cpp
+++ b/Source/core/workers/WorkerThread.cpp
@@ -137,12 +137,14 @@ void WorkerThread::workerThread()
 
     ThreadIdentifier threadID = m_threadID;
 
-#if !ENABLE_OILPAN
-    ASSERT(m_workerGlobalScope->hasOneRef());
-#endif
-
     // The below assignment will destroy the context, which will in turn notify messaging proxy.
     // We cannot let any objects survive past thread exit, because no other thread will run GC or otherwise destroy them.
+    // If Oilpan is enabled, we detach of the context/global scope, with the final heap cleanup below sweeping it out.
+#if ENABLE(OILPAN)
+    m_workerGlobalScope->dispose();
+#else
+    ASSERT(m_workerGlobalScope->hasOneRef());
+#endif
     m_workerGlobalScope = nullptr;
 
     ThreadState::detach();