Only set types of conditional expressions in strong mode.

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 848 matching lines @@
     push(new KernelLogicalExpression(receiver, token.stringValue, argument));
   }
 
   /// Handle `a ?? b`.
   void doIfNull(Token token) {
     Expression b = popForValue();
     Expression a = popForValue();
     VariableDeclaration variable = new VariableDeclaration.forValue(a);
     push(new KernelIfNullExpression(
         variable,
-        new KernelConditionalExpression(
+        new ConditionalExpression(
             buildIsNull(new VariableGet(variable), offsetForToken(token)),
             b,
-            new VariableGet(variable))));
+            new VariableGet(variable),
+            null)));
   }
 
   /// Handle `a?.b(...)`.
   void doIfNotNull(Token token) {
     IncompleteSend send = pop();
     push(send.withReceiver(pop(), token.charOffset, isNullAware: true));
   }
 
   void doDotOrCascadeExpression(Token token) {
     // TODO(ahe): Handle null-aware.
@@ skipping 2312 matching lines @@
     }
     if (isNullAware) {
       VariableDeclaration variable = new VariableDeclaration.forValue(receiver);
       return new KernelNullAwareMethodInvocation(
           variable,
           new ConditionalExpression(
               buildIsNull(new VariableGet(variable), offset),
               new NullLiteral(),
               new MethodInvocation(new VariableGet(variable), name, arguments)
                 ..fileOffset = offset,
-              const DynamicType())
+              null)
             ..fileOffset = offset)
         ..fileOffset = offset;
     } else {
       return new KernelMethodInvocation(receiver, name, arguments,
           isImplicitCall: isImplicitCall)
         ..fileOffset = offset;
     }
   }
 
   @override
@@ skipping 457 matching lines @@
     if (starToken == null) {
       return AsyncMarker.Async;
     } else {
       assert(identical(starToken.stringValue, "*"));
       return AsyncMarker.AsyncStar;
     }
   } else {
     return internalError("Unknown async modifier: $asyncToken");
   }
 }