Make the RuntimeTest use Runtime instances instead of its constituents.

Change-Id: I1005f279259917ff07d24e3bcd3643992ec8e3bd
diff --git a/src/runtime.h b/src/runtime.h
index da773a3..b57f1cf 100644
--- a/src/runtime.h
+++ b/src/runtime.h
@@ -39,6 +39,10 @@
 
   ~Runtime();
 
+  ClassLinker* GetClassLinker() {
+    return class_linker_;
+  }
+
  private:
   static void PlatformAbort(const char*, int);