Terminate worker threads before detaching main thread.

Source/web/WebKit.cpp

Index: Source/web/WebKit.cpp
diff --git a/Source/web/WebKit.cpp b/Source/web/WebKit.cpp
index 34fbaeb5d5ba7b163fa35f54a3cbc5eb9d9f0530..a6d8754f039f03651bf6d9c7c4ae1cc86cba318e 100644
--- a/Source/web/WebKit.cpp
+++ b/Source/web/WebKit.cpp
@@ -208,6 +208,11 @@ void shutdown()
     v8::Isolate* isolate = V8PerIsolateData::mainThreadIsolate();
     V8PerIsolateData::willBeDestroyed(isolate);
 
+    // Make sure we stop WorkerThreads before the main thread's ThreadState
+    // and later shutdown steps starts freeing up resources needed during
+    // worker termination.
+    WorkerThread::terminateAndWaitForAllWorkers();
+
     // Detach the main thread before starting the shutdown sequence
     // so that the main thread won't get involved in a GC during the shutdown.
     ThreadState::detachMainThread();