blink::shutdown() should not touch a message loop

Source/web/WebKit.cpp

Index: Source/web/WebKit.cpp
diff --git a/Source/web/WebKit.cpp b/Source/web/WebKit.cpp
index 115b9574ed6922873d187687acef7401b507f8de..b29de6b6a3f9622346a4453a2f4415126e799eae 100644
--- a/Source/web/WebKit.cpp
+++ b/Source/web/WebKit.cpp
@@ -181,8 +181,9 @@ void shutdown()
 {
     // currentThread will always be non-null in production, but can be null in Chromium unit tests.
     if (Platform::current()->currentThread()) {
-        ASSERT(s_endOfTaskRunner);
-        Platform::current()->currentThread()->removeTaskObserver(s_endOfTaskRunner);
+        // We don't need to (cannot) remove s_endOfTaskRunner from the current
+        // message loop, because the message loop is already destructed before
+        // the shutdown() is called.
         delete s_endOfTaskRunner;
         s_endOfTaskRunner = 0;
     }