Add type inference for null-aware method invocations.

pkg/front_end/lib/src/fasta/type_inference/type_inference_listener.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.md file.
 
 import 'package:front_end/src/fasta/type_inference/type_inference_engine.dart';
 import 'package:kernel/ast.dart';
 
 /// Base class for [TypeInferenceListener] that defines the API for debugging.
 ///
 /// By default no debug info is printed.  To enable debug printing, mix in
@@ skipping 193 matching lines @@
 
   void listLiteralExit(ListLiteral expression, DartType inferredType) =>
       debugExpressionExit("listLiteral", expression, inferredType);
 
   bool mapLiteralEnter(MapLiteral expression, DartType typeContext) =>
       debugExpressionEnter("mapLiteral", expression, typeContext);
 
   void mapLiteralExit(MapLiteral expression, DartType typeContext) =>
       debugExpressionExit("mapLiteral", expression, typeContext);
 
-  bool methodInvocationEnter(
-          MethodInvocation expression, DartType typeContext) =>
+  bool methodInvocationEnter(Expression expression, DartType typeContext) =>
       debugExpressionEnter("methodInvocation", expression, typeContext);
 
-  void methodInvocationExit(
-          MethodInvocation expression, DartType inferredType) =>
+  void methodInvocationExit(Expression expression, DartType inferredType) =>
       debugExpressionExit("methodInvocation", expression, inferredType);
 
   bool notEnter(Not expression, DartType typeContext) =>
       debugExpressionEnter("not", expression, typeContext);
 
   void notExit(Not expression, DartType inferredType) =>
       debugExpressionExit("not", expression, inferredType);
 
   bool nullLiteralEnter(NullLiteral expression, DartType typeContext) =>
       debugExpressionEnter("nullLiteral", expression, typeContext);
@@ skipping 91 matching lines @@
 
   void variableSetExit(VariableSet expression, DartType inferredType) =>
       debugExpressionExit("variableSet", expression, inferredType);
 
   void yieldStatementEnter(YieldStatement statement) =>
       debugStatementEnter('yieldStatement', statement);
 
   void yieldStatementExit(YieldStatement statement) =>
       debugStatementExit('yieldStatement', statement);
 }