ART: Add dex::StringIndex

Add abstraction for uint32_t string index.

Test: m test-art-host
Change-Id: I917c2881702fe3df112c713f06980f2278ced7ed
diff --git a/runtime/dex_file_test.cc b/runtime/dex_file_test.cc
index f94d07b..0fec856 100644
--- a/runtime/dex_file_test.cc
+++ b/runtime/dex_file_test.cc
@@ -418,7 +418,7 @@
     const char* type_str = java_lang_dex_file_->StringByTypeIdx(dex::TypeIndex(i));
     const DexFile::StringId* type_str_id = java_lang_dex_file_->FindStringId(type_str);
     ASSERT_TRUE(type_str_id != nullptr);
-    uint32_t type_str_idx = java_lang_dex_file_->GetIndexForStringId(*type_str_id);
+    dex::StringIndex type_str_idx = java_lang_dex_file_->GetIndexForStringId(*type_str_id);
     const DexFile::TypeId* type_id = java_lang_dex_file_->FindTypeId(type_str_idx);
     ASSERT_EQ(type_id, java_lang_dex_file_->FindTypeId(type_str));
     ASSERT_TRUE(type_id != nullptr);