Update V8 to r6190 as required by WebKit r75315

Change-Id: I0b2f598e4d8748df417ad350fc47a1c465ad1fef
diff --git a/src/d8-debug.h b/src/d8-debug.h
index c7acc2f..4e33e6f 100644
--- a/src/d8-debug.h
+++ b/src/d8-debug.h
@@ -98,7 +98,8 @@
 class ReceiverThread: public i::Thread {
  public:
   explicit ReceiverThread(RemoteDebugger* remote_debugger)
-      : remote_debugger_(remote_debugger) {}
+      : Thread("d8:ReceiverThrd"),
+        remote_debugger_(remote_debugger) {}
   ~ReceiverThread() {}
 
   void Run();
@@ -112,7 +113,8 @@
 class KeyboardThread: public i::Thread {
  public:
   explicit KeyboardThread(RemoteDebugger* remote_debugger)
-      : remote_debugger_(remote_debugger) {}
+      : Thread("d8:KeyboardThrd"),
+        remote_debugger_(remote_debugger) {}
   ~KeyboardThread() {}
 
   void Run();