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 37399f545ca475db1e18cd29ce91cdf00fed7e81..3e90beee8eacb41d69208bac01aa871b946bbcec 100644
--- a/third_party/WebKit/Source/platform/heap/Persistent.h
+++ b/third_party/WebKit/Source/platform/heap/Persistent.h
@@ -224,6 +224,14 @@ private:
 
     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(m_persistentNode);