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/entrypoints/entrypoint_utils.h b/runtime/entrypoints/entrypoint_utils.h
index 77eec46..8d419f8 100644
--- a/runtime/entrypoints/entrypoint_utils.h
+++ b/runtime/entrypoints/entrypoint_utils.h
@@ -30,14 +30,14 @@
 namespace art {
 
 namespace mirror {
-  class Class;
   class Array;
-  class ArtField;
   class ArtMethod;
+  class Class;
   class Object;
   class String;
 }  // namespace mirror
 
+class ArtField;
 class ScopedObjectAccessAlreadyRunnable;
 class Thread;
 
@@ -132,7 +132,7 @@
 };
 
 template<FindFieldType type, bool access_check>
-inline mirror::ArtField* FindFieldFromCode(uint32_t field_idx, mirror::ArtMethod* referrer,
+inline ArtField* FindFieldFromCode(uint32_t field_idx, mirror::ArtMethod* referrer,
                                            Thread* self, size_t expected_size)
     SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
@@ -143,7 +143,7 @@
     SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
 
 // Fast path field resolution that can't initialize classes or throw exceptions.
-inline mirror::ArtField* FindFieldFast(uint32_t field_idx,
+inline ArtField* FindFieldFast(uint32_t field_idx,
                                        mirror::ArtMethod* referrer,
                                        FindFieldType type, size_t expected_size)
     SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);