Add MultiSourceInformationStrategy

pkg/compiler/lib/src/js/js_source_mapping.dart

Index: pkg/compiler/lib/src/js/js_source_mapping.dart
diff --git a/pkg/compiler/lib/src/js/js_source_mapping.dart b/pkg/compiler/lib/src/js/js_source_mapping.dart
index 11278374bf815195faf6b967a368e465e979b0fb..bef8c191a39e836f7ebbcbae6d5d8995cb9982d4 100644
--- a/pkg/compiler/lib/src/js/js_source_mapping.dart
+++ b/pkg/compiler/lib/src/js/js_source_mapping.dart
@@ -4,7 +4,8 @@
 
 library js.source_mapping;
 
-import '../io/code_output.dart' show BufferedCodeOutput, SourceLocations;
+import '../io/code_output.dart'
+    show BufferedCodeOutput, SourceLocations, SourceLocationsProvider;
 import '../io/source_information.dart'
     show SourceLocation, SourceInformation, SourceInformationStrategy;
 import 'js.dart';
@@ -15,12 +16,24 @@ class JavaScriptSourceInformationStrategy extends SourceInformationStrategy {
   const JavaScriptSourceInformationStrategy();
 
   /// Creates a processor that can associate source information on [Node] with
-  /// code offsets in the [sourceMapper].
-  SourceInformationProcessor createProcessor(SourceMapper sourceMapper) {
+  /// code offsets in a [SourceMapper] provided by [sourceMapperProvider].
+  /// Source information for each [Node] is provider by [reader].
+  SourceInformationProcessor createProcessor(
+      SourceMapperProvider sourceMapperProvider,
+      SourceInformationReader reader) {
     return const SourceInformationProcessor();
   }
 }
 
+/// Interface for deriving [SourceInformation] from a [Node].
+///
+/// The base implementation read the value of the node itself.
+class SourceInformationReader {
+  const SourceInformationReader();
+
+  SourceInformation getSourceInformation(Node node) => node.sourceInformation;
+}
+
 /// An observer of code positions of printed JavaScript [Node]s.
 class CodePositionListener {
   const CodePositionListener();
@@ -38,6 +51,23 @@ class CodePositionListener {
       Node node, int startPosition, int endPosition, int closingPosition) {}
 }
 
+/// Interface for creating [SourceMapper]s for multiple source information
+/// engines.
+abstract class SourceMapperProvider {
+  SourceMapper createSourceMapper(String name);
+}
+
+/// Base implementation of [SourceMapperProvider].
+class SourceMapperProviderImpl implements SourceMapperProvider {
+  final SourceLocationsProvider provider;
+
+  SourceMapperProviderImpl(this.provider);
+
+  SourceMapper createSourceMapper(String name) {
+    return new SourceLocationsMapper(provider.createSourceLocations(name));
+  }
+}
+
 /// An interface for mapping code offsets with [SourceLocation]s for JavaScript
 /// [Node]s.
 abstract class SourceMapper {