ART: Add dex::StringIndex

Add abstraction for uint32_t string index.

Test: m test-art-host
Change-Id: I917c2881702fe3df112c713f06980f2278ced7ed
diff --git a/compiler/linker/relative_patcher_test.h b/compiler/linker/relative_patcher_test.h
index 0151789..233daf4 100644
--- a/compiler/linker/relative_patcher_test.h
+++ b/compiler/linker/relative_patcher_test.h
@@ -163,7 +163,8 @@
                                                offset + patch.LiteralOffset(),
                                                target_offset);
           } else if (patch.GetType() == LinkerPatch::Type::kStringRelative) {
-            uint32_t target_offset = string_index_to_offset_map_.Get(patch.TargetStringIndex());
+            uint32_t target_offset =
+                string_index_to_offset_map_.Get(patch.TargetStringIndex().index_);
             patcher_->PatchPcRelativeReference(&patched_code_,
                                                patch,
                                                offset + patch.LiteralOffset(),