The very first bits of resynthesizing elements from kernels.

pkg/front_end/lib/src/fasta/messages.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.messages;
 
 import 'dart:io' show exitCode;
 
 import 'package:kernel/ast.dart' show Library, Location, Program, TreeNode;
 
 import 'util/relativize.dart' show relativizeUri;
 
 import 'compiler_context.dart' show CompilerContext;
 
-import 'deprecated_problems.dart' show deprecated_InputError;
+import 'deprecated_problems.dart'
+    show deprecated_InputError, temporaryUntilPrintsRemovedEnablePrinting;
 
 import 'colors.dart' show cyan, magenta;
 
 import 'fasta_codes.dart' show Message;
 
 export 'fasta_codes.dart';
 
 const bool hideWarnings = false;
 
 bool get errorsAreFatal => CompilerContext.current.options.errorsAreFatal;
 
 bool get nitsAreFatal => CompilerContext.current.options.nitsAreFatal;
 
 bool get warningsAreFatal => CompilerContext.current.options.warningsAreFatal;
 
 bool get isVerbose => CompilerContext.current.options.verbose;
 
 bool get hideNits => !isVerbose;
 
 bool get setExitCodeOnProblem {
   return CompilerContext.current.options.setExitCodeOnProblem;
 }
 
 void warning(Message message, int charOffset, Uri uri) {
   if (hideWarnings) return;
-  print(deprecated_format(
-      uri, charOffset, colorWarning("Warning: ${message.message}")));
+  if (temporaryUntilPrintsRemovedEnablePrinting) {
+    print(deprecated_format(
+        uri, charOffset, colorWarning("Warning: ${message.message}")));
+  }
   if (warningsAreFatal) {
     if (isVerbose) print(StackTrace.current);
     throw new deprecated_InputError(
         uri, charOffset, "Compilation aborted due to fatal warnings.");
   }
 }
 
 void nit(Message message, int charOffset, Uri uri) {
   if (hideNits) return;
   print(
@@ skipping 70 matching lines @@
       program.libraries.clear();
       parent.parent = null;
       return result;
     } else {
       return null;
     }
   } else {
     return node.location;
   }
 }