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

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

Index: pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart b/pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart
index 5eea63328e1fb554cb1da106f990624b210683e0..3abae19a2435cb32b65a66e9bb186d51a98058de 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart
@@ -684,8 +684,6 @@ class KernelFactoryConstructorInvocation extends StaticInvocation
 
 /// Concrete shadow object representing a field in kernel form.
 class KernelField extends Field {
-  bool _implicitlyTyped = true;
-
   FieldNode _fieldNode;
 
   bool _isInferred = false;
@@ -694,12 +692,6 @@ class KernelField extends Field {
 
   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;
@@ -1913,16 +1905,6 @@ class KernelTypeInferenceEngine extends TypeInferenceEngineImpl {
         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;