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/image.cc b/runtime/image.cc
index 3cb2580..2d8c1c4 100644
--- a/runtime/image.cc
+++ b/runtime/image.cc
@@ -24,10 +24,12 @@
 namespace art {
 
 const uint8_t ImageHeader::kImageMagic[] = { 'a', 'r', 't', '\n' };
-const uint8_t ImageHeader::kImageVersion[] = { '0', '1', '4', '\0' };
+const uint8_t ImageHeader::kImageVersion[] = { '0', '1', '5', '\0' };
 
 ImageHeader::ImageHeader(uint32_t image_begin,
                          uint32_t image_size,
+                         uint32_t art_fields_offset,
+                         uint32_t art_fields_size,
                          uint32_t image_bitmap_offset,
                          uint32_t image_bitmap_size,
                          uint32_t image_roots,
@@ -39,6 +41,8 @@
                          bool compile_pic)
   : image_begin_(image_begin),
     image_size_(image_size),
+    art_fields_offset_(art_fields_offset),
+    art_fields_size_(art_fields_size),
     image_bitmap_offset_(image_bitmap_offset),
     image_bitmap_size_(image_bitmap_size),
     oat_checksum_(oat_checksum),