ART: Add dex::StringIndex

Add abstraction for uint32_t string index.

Test: m test-art-host
Change-Id: I917c2881702fe3df112c713f06980f2278ced7ed
diff --git a/compiler/compiled_method.h b/compiler/compiled_method.h
index 174e85e..bbf9eee 100644
--- a/compiler/compiled_method.h
+++ b/compiler/compiled_method.h
@@ -315,11 +315,11 @@
     return target_dex_file_;
   }
 
-  uint32_t TargetStringIndex() const {
+  dex::StringIndex TargetStringIndex() const {
     DCHECK(patch_type_ == Type::kString ||
            patch_type_ == Type::kStringRelative ||
            patch_type_ == Type::kStringBssEntry);
-    return string_idx_;
+    return dex::StringIndex(string_idx_);
   }
 
   const DexFile* TargetDexCacheDexFile() const {