Compute source spans for IR nodes and J/K-elements

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

Index: pkg/compiler/lib/src/js_backend/element_strategy.dart
diff --git a/pkg/compiler/lib/src/js_backend/element_strategy.dart b/pkg/compiler/lib/src/js_backend/element_strategy.dart
index 69864ea84011cfc8a5c20a4c6ff7c46789bf77c3..33967d1f3cc05f77a998d3a32f92551b3588e8dd 100644
--- a/pkg/compiler/lib/src/js_backend/element_strategy.dart
+++ b/pkg/compiler/lib/src/js_backend/element_strategy.dart
@@ -22,6 +22,7 @@ import '../js/js_source_mapping.dart' show JavaScriptSourceInformationStrategy;
 import '../js_backend/backend.dart';
 import '../js_backend/native_data.dart';
 import '../js_emitter/sorter.dart';
+import '../resolution/resolution_strategy.dart';
 import '../ssa/builder.dart';
 import '../ssa/rasta_ssa_builder_task.dart';
 import '../ssa/ssa.dart';
@@ -32,7 +33,8 @@ import '../world.dart';
 
 /// Strategy for using the [Element] model from the resolver as the backend
 /// model.
-class ElementBackendStrategy implements BackendStrategy {
+class ElementBackendStrategy extends ComputeSpannableMixin
+    implements BackendStrategy {
   final Compiler _compiler;
   final ClosureConversionTask closureDataLookup;
   SourceInformationStrategy _sourceInformationStrategy;