Fully implement string interning.

Also, more const.

Change-Id: I09cae88d677e8e6e42d0fa9b5d1093c79d225e66
diff --git a/src/compiler_test.cc b/src/compiler_test.cc
index 63881fd..eca5b2a 100644
--- a/src/compiler_test.cc
+++ b/src/compiler_test.cc
@@ -128,7 +128,7 @@
   DexCache* dex_cache = class_linker_->FindDexCache(*dex);
   EXPECT_EQ(dex->NumStringIds(), dex_cache->NumStrings());
   for (size_t i = 0; i < dex_cache->NumStrings(); i++) {
-    String* string = dex_cache->GetResolvedString(i);
+    const String* string = dex_cache->GetResolvedString(i);
     EXPECT_TRUE(string != NULL);
   }
   EXPECT_EQ(dex->NumTypeIds(), dex_cache->NumResolvedTypes());