Keep original order of fields in Class.

The fields of a class are ordered alphabetically in the dex
file. Keep the same order in the field arrays so that we can
do binary search lookups by name. Those lookups will be
implemented in a subsequent change in libcore/.

Bug: 18211592

(cherry picked from commit bfa3ed0ad988e1da13626ddbaf6dcae0c58ea79e)

Change-Id: I8f979de62ffe37d1c7d5c721717d2f3501e7c9e6
diff --git a/compiler/image_writer.cc b/compiler/image_writer.cc
index cf2cddb..b7283a4 100644
--- a/compiler/image_writer.cc
+++ b/compiler/image_writer.cc
@@ -484,13 +484,14 @@
   }
   //
   size_t num_reference_fields = h_class->NumReferenceInstanceFields();
+  MemberOffset field_offset = h_class->GetFirstReferenceInstanceFieldOffset();
   for (size_t i = 0; i < num_reference_fields; ++i) {
-    mirror::ArtField* field = h_class->GetInstanceField(i);
-    MemberOffset field_offset = field->GetOffset();
     mirror::Object* value = obj->GetFieldObject<mirror::Object>(field_offset);
     if (value != nullptr) {
       WalkFieldsInOrder(value);
     }
+    field_offset = MemberOffset(field_offset.Uint32Value() +
+                                sizeof(mirror::HeapReference<mirror::Object>));
   }
 }
 
@@ -507,13 +508,14 @@
     // Walk static fields of a Class.
     if (h_obj->IsClass()) {
       size_t num_static_fields = klass->NumReferenceStaticFields();
+      MemberOffset field_offset = klass->GetFirstReferenceStaticFieldOffset();
       for (size_t i = 0; i < num_static_fields; ++i) {
-        mirror::ArtField* field = klass->GetStaticField(i);
-        MemberOffset field_offset = field->GetOffset();
         mirror::Object* value = h_obj->GetFieldObject<mirror::Object>(field_offset);
         if (value != nullptr) {
           WalkFieldsInOrder(value);
         }
+        field_offset = MemberOffset(field_offset.Uint32Value() +
+                                    sizeof(mirror::HeapReference<mirror::Object>));
       }
     } else if (h_obj->IsObjectArray()) {
       // Walk elements of an object array.