Adds some code to help isolate where crash is happening

mojo/message_pump/message_pump_mojo.h

Index: mojo/message_pump/message_pump_mojo.h
diff --git a/mojo/message_pump/message_pump_mojo.h b/mojo/message_pump/message_pump_mojo.h
index d4028f143fbe2de9067159b41b413aac699bfa69..75ef47a17603d5c0128307fc8b877eb80058c05c 100644
--- a/mojo/message_pump/message_pump_mojo.h
+++ b/mojo/message_pump/message_pump_mojo.h
@@ -50,7 +50,8 @@ class MOJO_MESSAGE_PUMP_EXPORT MessagePumpMojo : public base::MessagePump {
   // Registers a MessagePumpMojoHandler for the specified handle. Only one
   // handler can be registered for a specified handle.
   // NOTE: a value of 0 for |deadline| indicates an indefinite timeout.
-  void AddHandler(MessagePumpMojoHandler* handler,
+  void AddHandler(int location,
+                  MessagePumpMojoHandler* handler,
                   const Handle& handle,
                   MojoHandleSignals wait_signals,
                   base::TimeTicks deadline);
@@ -72,8 +73,13 @@ class MOJO_MESSAGE_PUMP_EXPORT MessagePumpMojo : public base::MessagePump {
 
   // Contains the data needed to track a request to AddHandler().
   struct Handler {
-    Handler() : handler(NULL), wait_signals(MOJO_HANDLE_SIGNAL_NONE), id(0) {}
+    Handler()
+        : location(0),
+          handler(nullptr),
+          wait_signals(MOJO_HANDLE_SIGNAL_NONE),
+          id(0) {}
 
+    int location;
     MessagePumpMojoHandler* handler;
     MojoHandleSignals wait_signals;
     base::TimeTicks deadline;