Only attempt to do type inference on fields that lack a declared type.

pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart

 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /// This file declares a "shadow hierarchy" of concrete classes which extend
 /// the kernel class hierarchy, adding methods and fields needed by the
 /// BodyBuilder.
 ///
 /// Instances of these classes may be created using the factory methods in
 /// `ast_factory.dart`.
@@ skipping 666 matching lines @@
         _initialTarget.function.functionType,
         computeConstructorReturnType(_initialTarget),
         arguments);
     inferrer.listener.constructorInvocationExit(this, inferredType);
     return inferredType;
   }
 }
 
 /// Concrete shadow object representing a field in kernel form.
 class KernelField extends Field {
-  bool _implicitlyTyped = true;
-
   FieldNode _fieldNode;
 
   bool _isInferred = false;
 
   KernelTypeInferrer _typeInferrer;
 
   KernelField(Name name, {String fileUri}) : super(name, fileUri: fileUri) {}
 
-  @override
-  void set type(DartType value) {
-    _implicitlyTyped = false;
-    super.type = value;
-  }
-
   void _setInferredType(DartType inferredType) {
     _isInferred = true;
     super.type = inferredType;
   }
 }
 
 /// Concrete shadow object representing a for-in loop in kernel form.
 class KernelForInStatement extends ForInStatement implements KernelStatement {
   final bool _declaresVariable;
 
@@ skipping 1194 matching lines @@
   }
 
   @override
   KernelTypeInferrer createTopLevelTypeInferrer(TypeInferenceListener listener,
       InterfaceType thisType, KernelField field) {
     return field._typeInferrer =
         new KernelTypeInferrer._(this, field.fileUri, listener, true, thisType);
   }
 
   @override
-  bool fieldHasInitializer(KernelField field) {
-    return field.initializer != null;
-  }
-
-  @override
-  DartType getFieldDeclaredType(KernelField field) {
-    return field._implicitlyTyped ? null : field.type;
-  }
-
-  @override
   int getFieldOffset(KernelField field) {
     return field.fileOffset;
   }
 
   @override
   KernelTypeInferrer getFieldTypeInferrer(KernelField field) {
     return field._typeInferrer;
   }
 
   @override
@@ skipping 356 matching lines @@
   }
 
   transformChildren(v) {
     return internalError("Internal error: Unsupported operation.");
   }
 
   visitChildren(v) {
     return internalError("Internal error: Unsupported operation.");
   }
 }