Don't recreate CoreTypes in transformers. Pass it in.

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

Index: pkg/front_end/lib/src/fasta/fasta.dart
diff --git a/pkg/front_end/lib/src/fasta/fasta.dart b/pkg/front_end/lib/src/fasta/fasta.dart
index 6d1a2a37af246cc0054fb35b64a926073244d614..d75303f6f13798348df7dd62a1077216973c9963 100644
--- a/pkg/front_end/lib/src/fasta/fasta.dart
+++ b/pkg/front_end/lib/src/fasta/fasta.dart
@@ -16,6 +16,8 @@ import 'package:front_end/src/fasta/kernel/utils.dart';
 import 'package:kernel/binary/ast_to_binary.dart'
     show LibraryFilteringBinaryPrinter;
 
+import 'package:kernel/core_types.dart' show CoreTypes;
+
 import 'package:kernel/kernel.dart' show Library, Program, loadProgramFromBytes;
 
 import 'package:kernel/target/targets.dart' show Target, TargetFlags, getTarget;
@@ -220,8 +222,9 @@ Future<CompilationResult> parseScriptInFileSystem(
 
     // Perform target-specific transformations.
     Target target = getTarget("vm", new TargetFlags(strongMode: false));
-    target.performModularTransformations(program);
-    target.performGlobalTransformations(program);
+    CoreTypes coreTypes = new CoreTypes(program);

[ahe, 2017/05/29 14:08:46]

This has already been computed, so we shouldn't compute it again.

It's available as kernelTarget.loader.coreTypes in the above try-block.

[scheglov, 2017/05/30 00:06:10]

Fixed.
We now extract CoreTypes in addition to Program from KernelTarget.

+    target.performModularTransformations(coreTypes, program);
+    target.performGlobalTransformations(coreTypes, program);
 
     // Write the program to a list of bytes and return it.  Do not include
     // libraries that have a dart: import URI.