Add pause/resume for isolates in vmservice/observatory.

runtime/vm/message_handler.h

Index: runtime/vm/message_handler.h
diff --git a/runtime/vm/message_handler.h b/runtime/vm/message_handler.h
index eb1056b767abb3b7b3ba8eb396606101ebe313c0..dbc5d07a811ebe096681e2051be1cdd8cd001e3a 100644
--- a/runtime/vm/message_handler.h
+++ b/runtime/vm/message_handler.h
@@ -79,6 +79,12 @@ class MessageHandler {
     pause_on_start_ = pause_on_start;
   }
 
+  bool paused_on_start() const {
+    // If pause_on_start_ is still set, tell the user we are paused,
+    // even if we haven't hit the pause point yet.
+    return pause_on_start_;
+  }
+
   bool pause_on_exit() const {
     return pause_on_exit_;
   }