Add type inference for null-aware method invocations.

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

 // Copyright (c) 2016, 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.
 
 library fasta.body_builder;
 
 import '../fasta_codes.dart'
     show
         FastaMessage,
         codeConstFieldWithoutInitializer,
@@ skipping 20 matching lines @@
     hide InvalidExpression, InvalidInitializer, InvalidStatement;
 
 import 'package:kernel/clone.dart' show CloneVisitor;
 
 import 'package:kernel/transformations/flags.dart' show TransformerFlag;
 
 import 'package:kernel/class_hierarchy.dart' show ClassHierarchy;
 
 import 'package:kernel/core_types.dart' show CoreTypes;
 
-import 'frontend_accessors.dart' show buildIsNull, makeBinary, makeLet;
+import 'frontend_accessors.dart' show buildIsNull, makeBinary;
 
 import '../../scanner/token.dart' show BeginToken, Token;
 
 import '../scanner/token.dart' show isBinaryOperator, isMinusOperator;
 
 import '../errors.dart' show InputError, formatUnexpected, internalError;
 
 import '../source/scope_listener.dart'
     show JumpTargetKind, NullValue, ScopeListener;
 
@@ skipping 3136 matching lines @@
   Expression buildMethodInvocation(
       Expression receiver, Name name, Arguments arguments, int offset,
       {bool isConstantExpression: false,
       bool isNullAware: false,
       bool isImplicitCall: false}) {
     if (constantExpressionRequired && !isConstantExpression) {
       return buildCompileTimeError("Not a constant expression.", offset);
     }
     if (isNullAware) {
       VariableDeclaration variable = new VariableDeclaration.forValue(receiver);
-      return makeLet(
+      return new KernelNullAwareMethodInvocation(
           variable,
-          new KernelConditionalExpression(
+          new ConditionalExpression(
               buildIsNull(new VariableGet(variable), offset),
               new NullLiteral(),
               new MethodInvocation(new VariableGet(variable), name, arguments)
-                ..fileOffset = offset));
+                ..fileOffset = offset,
+              const DynamicType())
+            ..fileOffset = offset)
+        ..fileOffset = offset;
     } else {
       return new KernelMethodInvocation(receiver, name, arguments,
           isImplicitCall: isImplicitCall)
         ..fileOffset = offset;
     }
   }
 
   @override
   void addCompileTimeErrorFromMessage(FastaMessage message) {
     library.addCompileTimeError(message.charOffset, message.message,
@@ skipping 455 matching lines @@
     if (starToken == null) {
       return AsyncMarker.Async;
     } else {
       assert(identical(starToken.stringValue, "*"));
       return AsyncMarker.AsyncStar;
     }
   } else {
     return internalError("Unknown async modifier: $asyncToken");
   }
 }