ART: Add dex::StringIndex

Add abstraction for uint32_t string index.

Test: m test-art-host
Change-Id: I917c2881702fe3df112c713f06980f2278ced7ed
diff --git a/compiler/driver/compiler_driver.cc b/compiler/driver/compiler_driver.cc
index ad75ec4..42e5db3 100644
--- a/compiler/driver/compiler_driver.cc
+++ b/compiler/driver/compiler_driver.cc
@@ -842,9 +842,9 @@
     switch (inst->Opcode()) {
       case Instruction::CONST_STRING:
       case Instruction::CONST_STRING_JUMBO: {
-        uint32_t string_index = (inst->Opcode() == Instruction::CONST_STRING)
+        dex::StringIndex string_index((inst->Opcode() == Instruction::CONST_STRING)
             ? inst->VRegB_21c()
-            : inst->VRegB_31c();
+            : inst->VRegB_31c());
         mirror::String* string = class_linker->ResolveString(dex_file, string_index, dex_cache);
         CHECK(string != nullptr) << "Could not allocate a string when forcing determinism";
         break;