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/mirror/field.cc b/runtime/mirror/field.cc
index 82cc26e..70311bb 100644
--- a/runtime/mirror/field.cc
+++ b/runtime/mirror/field.cc
@@ -55,7 +55,7 @@
 
 ArtField* Field::GetArtField() {
   mirror::DexCache* const dex_cache = GetDeclaringClass()->GetDexCache();
-  mirror::ArtField* const art_field = dex_cache->GetResolvedField(GetDexFieldIndex());
+  ArtField* const art_field = dex_cache->GetResolvedField(GetDexFieldIndex(), sizeof(void*));
   CHECK(art_field != nullptr);
   return art_field;
 }