Stop calling Persistent::uninitialize after blink::shutdown is called.

third_party/WebKit/Source/platform/heap/Persistent.h

Index: third_party/WebKit/Source/platform/heap/Persistent.h
diff --git a/third_party/WebKit/Source/platform/heap/Persistent.h b/third_party/WebKit/Source/platform/heap/Persistent.h
index 36539c7efee59f111a0f3b4660e7ed5291eaf188..d75044be3019b76d627e3c72f133a09d1f9e3b25 100644
--- a/third_party/WebKit/Source/platform/heap/Persistent.h
+++ b/third_party/WebKit/Source/platform/heap/Persistent.h
@@ -227,6 +227,14 @@ class PersistentBase {
   }
 
   void uninitialize() {
+    // TODO(haraken): This is a short-term hack to prevent use-after-frees
+    // during a shutdown sequence.
+    // 1) blink::shutdown() frees the underlying storage for persistent nodes.
+    // 2) ~MessageLoop() destructs some Chromium-side objects that hold
+    //    Persistent. It touches the underlying storage and crashes.
+    if (WTF::isShutdown())
+      return;
+
     if (crossThreadnessConfiguration == CrossThreadPersistentConfiguration) {
       if (acquireLoad(reinterpret_cast<void* volatile*>(&m_persistentNode)))
         ProcessHeap::crossThreadPersistentRegion().freePersistentNode(