Move dexCacheStrings from ArtMethod to Class

Adds one load for const strings which are not direct.

Saves >= 60KB of memory avg per app.
Image size: -350KB.

Bug: 17643507
Change-Id: I2d1a3253d9de09682be9bc6b420a29513d592cc8

(cherry picked from commit f521f423b66e952f746885dd9f6cf8ef2788955d)
diff --git a/compiler/image_writer.cc b/compiler/image_writer.cc
index 03899cc..3b1d914 100644
--- a/compiler/image_writer.cc
+++ b/compiler/image_writer.cc
@@ -967,7 +967,7 @@
   if (obj->IsArtMethod()) {
     // Size without pointer fields since we don't want to overrun the buffer if target art method
     // is 32 bits but source is 64 bits.
-    n = mirror::ArtMethod::SizeWithoutPointerFields();
+    n = mirror::ArtMethod::SizeWithoutPointerFields(sizeof(void*));
   } else {
     n = obj->SizeOf();
   }