Syntax clean up to make clang happy.

Change-Id: I0984c395bbd1ee4b206eafd19915b6f68781dd16
diff --git a/src/jdwp/jdwp.h b/src/jdwp/jdwp.h
index b80033c..725e857 100644
--- a/src/jdwp/jdwp.h
+++ b/src/jdwp/jdwp.h
@@ -31,8 +31,8 @@
 
 namespace art {
 
-struct Method;
-struct Thread;
+class Method;
+class Thread;
 
 namespace JDWP {