Move mirror::ArtMethod to native

Optimizing + quick tests are passing, devices boot.

TODO: Test and fix bugs in mips64.

Saves 16 bytes per most ArtMethod, 7.5MB reduction in system PSS.
Some of the savings are from removal of virtual methods and direct
methods object arrays.

Bug: 19264997
Change-Id: I622469a0cfa0e7082a2119f3d6a9491eb61e3f3d
diff --git a/runtime/read_barrier.h b/runtime/read_barrier.h
index 52d83a2..aa72e97 100644
--- a/runtime/read_barrier.h
+++ b/runtime/read_barrier.h
@@ -28,12 +28,11 @@
 // which needs to be a C header file for asm_support.h.
 
 namespace art {
-
 namespace mirror {
-  class ArtMethod;
   class Object;
   template<typename MirrorType> class HeapReference;
 }  // namespace mirror
+class ArtMethod;
 
 class ReadBarrier {
  public: