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

pkg/compiler/lib/src/backend_strategy.dart

 // Copyright (c) 2017, 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 dart2js.backend_strategy;
 
 import 'closure.dart' show ClosureConversionTask;
+import 'common.dart';
 import 'common/tasks.dart';
 import 'enqueue.dart';
+import 'elements/entities.dart';
 import 'io/source_information.dart';
 import 'js_backend/js_backend.dart';
 import 'js_backend/native_data.dart';
 import 'js_emitter/sorter.dart';
 import 'ssa/ssa.dart';
 import 'universe/world_builder.dart';
 import 'world.dart';
 
 /// Strategy pattern that defines the element model used in type inference
 /// and code generation.
@@ skipping 16 matching lines @@
 
   /// Creates the [WorkItemBuilder] used by the codegen enqueuer.
   WorkItemBuilder createCodegenWorkItemBuilder(ClosedWorld closedWorld);
 
   /// Creates the [SsaBuilder] used for the element model.
   SsaBuilder createSsaBuilder(CompilerTask task, JavaScriptBackend backend,
       SourceInformationStrategy sourceInformationStrategy);
 
   /// Returns the [SourceInformationStrategy] use for the element model.
   SourceInformationStrategy get sourceInformationStrategy;
+
+  /// Creates a [SourceSpan] from [spannable] in context of [currentElement].
+  SourceSpan spanFromSpannable(Spannable spannable, Entity currentElement);
 }