Mark more roots.

This is most of the stuff. (Everything that currently exists, though there's
more to come.)

Change-Id: I235a21b006820a027c494374a5b52ffefed89c32
diff --git a/src/runtime.h b/src/runtime.h
index 922eeab..6a5d755 100644
--- a/src/runtime.h
+++ b/src/runtime.h
@@ -101,7 +101,7 @@
     return java_vm_;
   }
 
-  void VisitRoots(Heap::RootVistor* root_visitor, void* arg) const;
+  void VisitRoots(Heap::RootVisitor* visitor, void* arg) const;
 
  private:
   static void PlatformAbort(const char*, int);