ART: Add dex::StringIndex

Add abstraction for uint32_t string index.

Test: m test-art-host
Change-Id: I917c2881702fe3df112c713f06980f2278ced7ed
diff --git a/compiler/optimizing/sharpening.cc b/compiler/optimizing/sharpening.cc
index a127708..daf160a 100644
--- a/compiler/optimizing/sharpening.cc
+++ b/compiler/optimizing/sharpening.cc
@@ -267,7 +267,7 @@
   DCHECK(!load_string->IsInDexCache());
 
   const DexFile& dex_file = load_string->GetDexFile();
-  uint32_t string_index = load_string->GetStringIndex();
+  dex::StringIndex string_index = load_string->GetStringIndex();
 
   HLoadString::LoadKind desired_load_kind = HLoadString::LoadKind::kDexCacheViaMethod;
   uint64_t address = 0u;  // String or dex cache element address.