Revert "Revert "Use interceptor convention for methods declared on native classes.""

sdk/lib/_internal/compiler/implementation/ssa/builder.dart

Index: sdk/lib/_internal/compiler/implementation/ssa/builder.dart
diff --git a/sdk/lib/_internal/compiler/implementation/ssa/builder.dart b/sdk/lib/_internal/compiler/implementation/ssa/builder.dart
index 6581cc0d1aa155e0ff85d309172f83ad12b8c942..1403fcd5472a7f1b77062de3c126ab4683cfe35f 100644
--- a/sdk/lib/_internal/compiler/implementation/ssa/builder.dart
+++ b/sdk/lib/_internal/compiler/implementation/ssa/builder.dart
@@ -321,8 +321,9 @@ class LocalsHandler {
         type = HType.UNKNOWN;
       } else if (cls != compiler.objectClass) {
         JavaScriptBackend backend = compiler.backend;
-        assert(!backend.isInterceptorClass(cls));
-        name = const SourceString('_');
+        if (!backend.isInterceptorClass(cls)) {
+          name = const SourceString('_');
+        }
       }
       Element parameter = new InterceptedElement(type, name, element);
       HParameterValue value = new HParameterValue(parameter);