Create an option to disable type inference and type promotion.

pkg/front_end/lib/src/fasta/source/diet_listener.dart

Index: pkg/front_end/lib/src/fasta/source/diet_listener.dart
diff --git a/pkg/front_end/lib/src/fasta/source/diet_listener.dart b/pkg/front_end/lib/src/fasta/source/diet_listener.dart
index 3c8d04174b8e08d7faa8d7bb0346307a94a4f5b6..ec1cd61e1b9835231519b9326ad5932a03de9179 100644
--- a/pkg/front_end/lib/src/fasta/source/diet_listener.dart
+++ b/pkg/front_end/lib/src/fasta/source/diet_listener.dart
@@ -10,6 +10,9 @@ import 'package:front_end/src/fasta/type_inference/type_inference_engine.dart'
 import 'package:front_end/src/fasta/type_inference/type_inference_listener.dart'
     show TypeInferenceListener;
 
+import 'package:front_end/src/fasta/type_inference/type_inferrer.dart'
+    show TypeInferrerDisabled;
+
 import 'package:kernel/ast.dart' show AsyncMarker, Class, InterfaceType;
 
 import 'package:kernel/class_hierarchy.dart' show ClassHierarchy;
@@ -416,8 +419,9 @@ class DietListener extends StackListener {
       Class cls = builder.parent.target;
       thisType = cls.thisType;
     }
-    var typeInferrer =
-        typeInferenceEngine.createLocalTypeInferrer(uri, listener, thisType);
+    var typeInferrer = library.disableTypeInference
+        ? new TypeInferrerDisabled()
+        : typeInferenceEngine.createLocalTypeInferrer(uri, listener, thisType);
     return new BodyBuilder(library, builder, memberScope, formalParameterScope,
         hierarchy, coreTypes, currentClass, isInstanceMember, uri, typeInferrer)
       ..constantExpressionRequired = builder.isConstructor && builder.isConst;