Address a few TODOs related to type propagation.

runtime/vm/flow_graph_builder.cc

Index: runtime/vm/flow_graph_builder.cc
===================================================================
--- runtime/vm/flow_graph_builder.cc	(revision 7715)
+++ runtime/vm/flow_graph_builder.cc	(working copy)
@@ -161,7 +161,10 @@
       context_value = new UseVal(load);
     }
     Computation* store = new NativeStoreFieldComp(
-        context_value, Context::variable_offset(local.index()), value);
+        context_value,
+        Context::variable_offset(local.index()),
+        value,
+        local.type());
     return store;
   } else {
     return new StoreLocalComp(local, value, owner()->context_level());