Fix for implicit null test for oat.

This change also cleans up the notion of the callee save method with a
"IsPhony" call. Stack visitors check whether the frame they are on has a
legitimate method with "HasMethod".

Change-Id: I8ac0fdd595c1e764fdc22cfa9c6a394595f7e141
diff --git a/src/thread.h b/src/thread.h
index 6f1bcc3..0be4aa6 100644
--- a/src/thread.h
+++ b/src/thread.h
@@ -130,6 +130,9 @@
     sp_ = sp;
   }
 
+  // Is this a frame for a real method (native or with dex code)
+  bool HasMethod() const;
+
  private:
   Method* NextMethod() const;