Split HForeign into HForeignCode and abstract base class.

pkg/compiler/lib/src/ssa/ssa_tracer.dart

Index: pkg/compiler/lib/src/ssa/ssa_tracer.dart
diff --git a/pkg/compiler/lib/src/ssa/ssa_tracer.dart b/pkg/compiler/lib/src/ssa/ssa_tracer.dart
index ebac199c2f0a63b839a95016984011b6fe5362a1..ccecc6720ed065c6a9a518460be23fa8f06c4e54 100644
--- a/pkg/compiler/lib/src/ssa/ssa_tracer.dart
+++ b/pkg/compiler/lib/src/ssa/ssa_tracer.dart
@@ -331,8 +331,9 @@ class HInstructionStringifier implements HVisitor<String> {
     return visitGenericInvoke("Invoke constructor body", target, invoke.inputs);
   }
 
-  String visitForeign(HForeign foreign) {
-    return visitGenericInvoke("Foreign", "${foreign.codeTemplate.ast}", foreign.inputs);
+  String visitForeignCode(HForeignCode foreign) {
+    return visitGenericInvoke("Foreign", "${foreign.codeTemplate.ast}",
+                              foreign.inputs);
   }
 
   String visitForeignNew(HForeignNew node) {