Move ArtField to native

Add linear alloc. Moved ArtField to be native object. Changed image
writer to put ArtFields after the mirror section.

Savings:
2MB on low ram devices
4MB on normal devices

Total PSS measurements before (normal N5, 95s after shell start):
Image size: 7729152 bytes
23112 kB: .NonMoving
23212 kB: .NonMoving
22868 kB: .NonMoving
23072 kB: .NonMoving
22836 kB: .NonMoving
19618 kB: .Zygote
19850 kB: .Zygote
19623 kB: .Zygote
19924 kB: .Zygote
19612 kB: .Zygote
Avg: 42745.4 kB

After:
Image size: 7462912 bytes
17440 kB: .NonMoving
16776 kB: .NonMoving
16804 kB: .NonMoving
17812 kB: .NonMoving
16820 kB: .NonMoving
18788 kB: .Zygote
18856 kB: .Zygote
19064 kB: .Zygote
18841 kB: .Zygote
18629 kB: .Zygote
3499 kB: .LinearAlloc
3408 kB: .LinearAlloc
3424 kB: .LinearAlloc
3600 kB: .LinearAlloc
3436 kB: .LinearAlloc
Avg: 39439.4 kB

No reflection performance changes.

Bug: 19264997
Bug: 17643507

Change-Id: I10c73a37913332080aeb978c7c94713bdfe4fe1c
diff --git a/runtime/reflection.h b/runtime/reflection.h
index ff970e5..c2d406a 100644
--- a/runtime/reflection.h
+++ b/runtime/reflection.h
@@ -23,18 +23,18 @@
 
 namespace art {
 namespace mirror {
-  class ArtField;
   class ArtMethod;
   class Class;
   class Object;
 }  // namespace mirror
+class ArtField;
 union JValue;
 class ScopedObjectAccessAlreadyRunnable;
 class ShadowFrame;
 
 mirror::Object* BoxPrimitive(Primitive::Type src_class, const JValue& value)
     SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
-bool UnboxPrimitiveForField(mirror::Object* o, mirror::Class* dst_class, mirror::ArtField* f,
+bool UnboxPrimitiveForField(mirror::Object* o, mirror::Class* dst_class, ArtField* f,
                             JValue* unboxed_value)
     SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 bool UnboxPrimitiveForResult(mirror::Object* o, mirror::Class* dst_class, JValue* unboxed_value)