Fully implement string interning.

Also, more const.

Change-Id: I09cae88d677e8e6e42d0fa9b5d1093c79d225e66
diff --git a/src/class_linker_test.cc b/src/class_linker_test.cc
index c403065..a34f180 100644
--- a/src/class_linker_test.cc
+++ b/src/class_linker_test.cc
@@ -262,7 +262,7 @@
     class_linker_->VisitRoots(TestRootVisitor, NULL);
   }
 
-  static void TestRootVisitor(Object* root, void* arg) {
+  static void TestRootVisitor(const Object* root, void* arg) {
     EXPECT_TRUE(root != NULL);
   }
 };