Fix type inference of assignments to local variables.

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 1251 matching lines @@
       bool isConst: false,
       bool isLocalFunction: false})
       : _implicitlyTyped = type == null,
         _isLocalFunction = isLocalFunction,
         super(name,
             initializer: initializer,
             type: type ?? const DynamicType(),
             isFinal: isFinal,
             isConst: isConst);
 
-  DartType get _declaredType => _implicitlyTyped ? null : type;
-
   @override
   void _inferStatement(KernelTypeInferrer inferrer) {
     inferrer.listener.variableDeclarationEnter(this);
     var declaredType = _implicitlyTyped ? null : type;
     if (initializer != null) {
       var inferredType = inferrer.inferDeclarationType(inferrer.inferExpression(
           initializer, declaredType, _implicitlyTyped));
       if (inferrer.strongMode && _implicitlyTyped) {
         inferrer.instrumentation?.record(Uri.parse(inferrer.uri), fileOffset,
             'type', new InstrumentationValueForType(inferredType));
@@ skipping 48 matching lines @@
   KernelVariableSet(VariableDeclaration variable, Expression value)
       : super(variable, value);
 
   @override
   DartType _inferExpression(
       KernelTypeInferrer inferrer, DartType typeContext, bool typeNeeded) {
     var variable = this.variable as KernelVariableDeclaration;
     typeNeeded =
         inferrer.listener.variableSetEnter(this, typeContext) || typeNeeded;
     var inferredType =
-        inferrer.inferExpression(value, variable._declaredType, typeNeeded);
+        inferrer.inferExpression(value, variable.type, typeNeeded);
     inferrer.listener.variableSetExit(this, inferredType);
     return inferredType;
   }
 }
 
 /// Concrete shadow object representing a yield statement in kernel form.
 class KernelYieldStatement extends YieldStatement implements KernelStatement {
   KernelYieldStatement(Expression expression, {bool isYieldStar: false})
       : super(expression, isYieldStar: isYieldStar);
 
@@ skipping 14 matching lines @@
                 ? inferrer.coreTypes.streamClass
                 : inferrer.coreTypes.iterableClass);
       }
     }
     var inferredType = inferrer.inferExpression(
         expression, typeContext, closureContext != null);
     closureContext?.handleYield(inferrer, isYieldStar, inferredType);
     inferrer.listener.yieldStatementExit(this);
   }
 }