Adds some code to help isolate where crash is happening

mojo/message_pump/handle_watcher.h

Index: mojo/message_pump/handle_watcher.h
diff --git a/mojo/message_pump/handle_watcher.h b/mojo/message_pump/handle_watcher.h
index 4f7115a8613fa75f81ebb0cd191dacd03845d0c9..5da816db2a8f5ba52d200b0621410b3c49eb6738 100644
--- a/mojo/message_pump/handle_watcher.h
+++ b/mojo/message_pump/handle_watcher.h
@@ -7,6 +7,7 @@
 
 #include "base/basictypes.h"
 #include "base/callback_forward.h"
+#include "base/location.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/run_loop.h"
 #include "mojo/message_pump/mojo_message_pump_export.h"
@@ -26,11 +27,13 @@ class HandleWatcherTest;
 // when the handle is ready, or the deadline has expired.
 class MOJO_MESSAGE_PUMP_EXPORT HandleWatcher {
  public:
-  HandleWatcher();
+  explicit HandleWatcher(int location);
 
   // The destructor implicitly stops listening. See Stop() for details.
   ~HandleWatcher();
 
+  int location() const { return location_; }
+
   // Starts listening for |handle|. This implicitly invokes Stop(). In other
   // words, Start() performs one asynchronous watch at a time. It is ok to call
   // Start() multiple times, but it cancels any existing watches. |callback| is
@@ -52,6 +55,8 @@ class MOJO_MESSAGE_PUMP_EXPORT HandleWatcher {
   class SameThreadWatchingState;
   class SecondaryThreadWatchingState;
 
+  const int location_;
+
   // If non-NULL Start() has been invoked.
   scoped_ptr<StateBase> state_;