Add MultiSourceInformationStrategy

pkg/compiler/lib/src/js_emitter/full_emitter/emitter.dart

Index: pkg/compiler/lib/src/js_emitter/full_emitter/emitter.dart
diff --git a/pkg/compiler/lib/src/js_emitter/full_emitter/emitter.dart b/pkg/compiler/lib/src/js_emitter/full_emitter/emitter.dart
index b101d2b51a3479263bf6655b2dfb1badaa2db154..532e940628cbc20bbc1a2f588d4f36111a5fc01d 100644
--- a/pkg/compiler/lib/src/js_emitter/full_emitter/emitter.dart
+++ b/pkg/compiler/lib/src/js_emitter/full_emitter/emitter.dart
@@ -1540,15 +1540,20 @@ class Emitter implements js_emitter.Emitter {
     }
 
     if (generateSourceMap) {
-      mainOutput.add(generateSourceMapTag(
+      mainOutput.add(SourceMapBuilder.generateSourceMapTag(
           compiler.options.sourceMapUri, compiler.options.outputUri));
     }
 
     mainOutput.close();
 
     if (generateSourceMap) {
-      outputSourceMap(mainOutput, lineColumnCollector, '',
-          compiler.options.sourceMapUri, compiler.options.outputUri);
+      SourceMapBuilder.outputSourceMap(
+          mainOutput,
+          lineColumnCollector,
+          '',
+          compiler.options.sourceMapUri,
+          compiler.options.outputUri,
+          compiler.outputProvider);
     }
   }
 
@@ -1639,17 +1644,6 @@ class Emitter implements js_emitter.Emitter {
     return outputBuffers.values.fold(0, (a, b) => a + b.length);
   }
 
-  String generateSourceMapTag(Uri sourceMapUri, Uri fileUri) {
-    if (sourceMapUri != null && fileUri != null) {
-      String sourceMapFileName = relativize(fileUri, sourceMapUri, false);
-      return '''
-
-//# sourceMappingURL=$sourceMapFileName
-''';
-    }
-    return '';
-  }
-
   ClassBuilder getElementDescriptor(Element element, Fragment fragment) {
     Element owner = element.library;
     if (!element.isLibrary &&
@@ -1898,9 +1892,10 @@ class Emitter implements js_emitter.Emitter {
               compiler.options.outputUri.replace(pathSegments: partSegments);
         }
 
-        output.add(generateSourceMapTag(mapUri, partUri));
+        output.add(SourceMapBuilder.generateSourceMapTag(mapUri, partUri));
         output.close();
-        outputSourceMap(output, lineColumnCollector, partName, mapUri, partUri);
+        SourceMapBuilder.outputSourceMap(output, lineColumnCollector, partName,
+            mapUri, partUri, compiler.outputProvider);
       } else {
         output.close();
       }
@@ -1917,21 +1912,6 @@ class Emitter implements js_emitter.Emitter {
     return new jsAst.Comment(generatedBy(compiler, flavor: options.join(", ")));
   }
 
-  void outputSourceMap(
-      CodeOutput output, LineColumnProvider lineColumnProvider, String name,
-      [Uri sourceMapUri, Uri fileUri]) {
-    if (!generateSourceMap) return;
-    // Create a source file for the compilation output. This allows using
-    // [:getLine:] to transform offsets to line numbers in [SourceMapBuilder].
-    SourceMapBuilder sourceMapBuilder =
-        new SourceMapBuilder(sourceMapUri, fileUri, lineColumnProvider);
-    output.forEachSourceLocation(sourceMapBuilder.addMapping);
-    String sourceMap = sourceMapBuilder.build();
-    compiler.outputProvider(name, 'js.map', OutputType.js_map)
-      ..add(sourceMap)
-      ..close();
-  }
-
   void outputDeferredMap() {
     Map<String, dynamic> mapping = new Map<String, dynamic>();
     // Json does not support comments, so we embed the explanation in the