dart2js: use correct Compiler class.

Review URL: https://codereview.chromium.org//1272613003 .
diff --git a/pkg/compiler/lib/src/js_emitter/headers.dart b/pkg/compiler/lib/src/js_emitter/headers.dart
index a8466ce..7906dd9 100644
--- a/pkg/compiler/lib/src/js_emitter/headers.dart
+++ b/pkg/compiler/lib/src/js_emitter/headers.dart
@@ -3,7 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 library dart2js.js_emitter.headers;
-import '../apiimpl.dart' show Compiler;
+import '../dart2jslib.dart' show Compiler;
 
 String generatedBy(Compiler compiler, {String flavor: ""}) {
   String suffix = '';