Convert String and List to abstract classes.

runtime/vm/flow_graph_compiler_x64.cc

Index: runtime/vm/flow_graph_compiler_x64.cc
diff --git a/runtime/vm/flow_graph_compiler_x64.cc b/runtime/vm/flow_graph_compiler_x64.cc
index 3ee9bd6f53a4839512670db517ea59abdc651249..622b30652cb3e26bf62bde729f69c997b1734833 100644
--- a/runtime/vm/flow_graph_compiler_x64.cc
+++ b/runtime/vm/flow_graph_compiler_x64.cc
@@ -152,7 +152,7 @@ FlowGraphCompiler::GenerateInstantiatedTypeWithArgumentsTest(
       __ cmpl(kClassIdReg, Immediate(type_class.id()));
       __ j(EQUAL, is_instance_lbl);
     }
-    if (type.IsListInterface()) {
+    if (type.IsListType()) {
       GenerateListTypeCheck(kClassIdReg, is_instance_lbl);
     }
     return GenerateSubtype1TestCacheLookup(
@@ -261,7 +261,7 @@ bool FlowGraphCompiler::GenerateInstantiatedTypeNoArgumentsTest(
         kClassIdReg, type, is_instance_lbl, is_not_instance_lbl);
     return false;
   }
-  if (type.IsStringInterface()) {
+  if (type.IsStringType()) {
     GenerateStringTypeCheck(kClassIdReg, is_instance_lbl, is_not_instance_lbl);
     return false;
   }