ART: Clean up includes.

Reduce dependencies to improve incremental build times.
Break up circular dependency involving class_linker-inl.h.

Change-Id: I4be742c5c2b5cd9855beea86630fd68aab76b0db
diff --git a/runtime/proxy_test.cc b/runtime/proxy_test.cc
index a3156b4..6061f73 100644
--- a/runtime/proxy_test.cc
+++ b/runtime/proxy_test.cc
@@ -18,6 +18,7 @@
 #include <vector>
 
 #include "art_field-inl.h"
+#include "class_linker-inl.h"
 #include "common_compiler_test.h"
 #include "scoped_thread_state_change.h"