Add more factory methods to FrontEndStrategy.

pkg/compiler/lib/src/js_backend/mirrors_data.dart

Index: pkg/compiler/lib/src/js_backend/mirrors_data.dart
diff --git a/pkg/compiler/lib/src/js_backend/mirrors_data.dart b/pkg/compiler/lib/src/js_backend/mirrors_data.dart
index 23462e95c514efa3971b4b894329e87e74f9ca0e..10528e24e4a9fc8d781301f8c1749c737f0b0389 100644
--- a/pkg/compiler/lib/src/js_backend/mirrors_data.dart
+++ b/pkg/compiler/lib/src/js_backend/mirrors_data.dart
@@ -207,10 +207,9 @@ class MirrorsDataImpl implements MirrorsData, MirrorsDataBuilder {
 
   final CommonElements _commonElements;
 
-  final JavaScriptConstantCompiler _constants;
+  MirrorsDataImpl(this._compiler, this._options, this._commonElements);
 
-  MirrorsDataImpl(
-      this._compiler, this._options, this._commonElements, this._constants);
+  JavaScriptConstantCompiler get _constants => _compiler.backend.constants;
 
   void registerUsedMember(MemberElement member) {
     if (member == _commonElements.disableTreeShakingMarker) {