ART: Rename ArtMethod JNI field

The field is multi-purpose, rename it to data and clean up
accessors in preparation of more checks.

Test: m test-art-host
Change-Id: Ib4b84b7b1a51ca201544bc488ce8770aa858c7fd
diff --git a/runtime/art_method.cc b/runtime/art_method.cc
index f86cb13..c4d961f 100644
--- a/runtime/art_method.cc
+++ b/runtime/art_method.cc
@@ -497,4 +497,12 @@
   hotness_count_ = 0;
 }
 
+bool ArtMethod::IsImagePointerSize(size_t pointer_size) {
+  Runtime* runtime = Runtime::Current();
+  if (runtime == nullptr) {
+    return true;
+  }
+  return runtime->GetClassLinker()->GetImagePointerSize() == pointer_size;
+}
+
 }  // namespace art