Revert "Switch profiler from isolates to threads"

runtime/vm/message_handler.cc

Index: runtime/vm/message_handler.cc
diff --git a/runtime/vm/message_handler.cc b/runtime/vm/message_handler.cc
index 30194cd5b4ec4a3074f690712f8bca1c2679a0b3..47ab4b9db7d4ef49dde0dc97e56e774319076820 100644
--- a/runtime/vm/message_handler.cc
+++ b/runtime/vm/message_handler.cc
@@ -183,6 +183,10 @@ MessageHandler::MessageStatus MessageHandler::HandleMessages(
   // If isolate() returns NULL StartIsolateScope does nothing.
   StartIsolateScope start_isolate(isolate());
 
+  // ThreadInterrupter may have gone to sleep while waiting for
+  // an isolate to start handling messages.
+  ThreadInterrupter::WakeUp();
+
   MessageStatus max_status = kOK;
   Message::Priority min_priority = ((allow_normal_messages && !paused())
                                     ? Message::kNormalPriority