Avoid read barriers for ArtMethod::GetDexFile

Shows up in pmd benchmark from Class::FindDeclaredDirectMethod and
Class::FindDeclaredVirtualMethod. There are still calls to
IsProxyMethod that could probably be eliminated.

ReadBarrier::Mark goes from 12.39% to 3.45% according to perf.

Test: test-art-host

Change-Id: I6a4f2fa2d68bf5f393f83b9b70e8d6fcc9dbdaa2
diff --git a/runtime/mirror/class.h b/runtime/mirror/class.h
index 7f6aa12..c9f27ad 100644
--- a/runtime/mirror/class.h
+++ b/runtime/mirror/class.h
@@ -722,7 +722,8 @@
 
   void DumpClass(std::ostream& os, int flags) REQUIRES_SHARED(Locks::mutator_lock_);
 
-  template<VerifyObjectFlags kVerifyFlags = kDefaultVerifyFlags>
+  template<VerifyObjectFlags kVerifyFlags = kDefaultVerifyFlags,
+           ReadBarrierOption kReadBarrierOption = kWithReadBarrier>
   DexCache* GetDexCache() REQUIRES_SHARED(Locks::mutator_lock_);
 
   // Also updates the dex_cache_strings_ variable from new_dex_cache.