Extend compiler API to support multiple outputs.

dart/sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart

 // Copyright (c) 2012, 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.
 
 part of js_backend;
 
 /**
  * A function element that represents a closure call. The signature is copied
  * from the given element.
  */
@@ skipping 2247 matching lines @@
       mainBuffer.add('$isolateProperties$_=$_{}$N');
       addDefineClassAndFinishClassFunctionsIfNecessary(mainBuffer);
       addLazyInitializerFunctionIfNecessary(mainBuffer);
       emitFinishIsolateConstructor(mainBuffer);
       mainBuffer.add('}\n');
       compiler.assembledCode = mainBuffer.getText();
 
       if (generateSourceMap) {
         SourceFile compiledFile = new SourceFile(null, compiler.assembledCode);
         String sourceMap = buildSourceMap(mainBuffer, compiledFile);
-        // TODO(podivilov): We should find a better way to return source maps to
-        // compiler. Using diagnostic handler for that purpose is a temporary
-        // hack.
-        compiler.reportDiagnostic(
-            null, sourceMap, new api.Diagnostic(-1, 'source map'));
+        compiler.outputProvider('', 'js.map')
+            ..add(sourceMap)
+            ..close();
       }
     });
     return compiler.assembledCode;
   }
 
   String buildSourceMap(CodeBuffer buffer, SourceFile compiledFile) {
     SourceMapBuilder sourceMapBuilder = new SourceMapBuilder();
     buffer.forEachSourceLocation(sourceMapBuilder.addMapping);
     return sourceMapBuilder.build(compiledFile);
   }
 }
 
 const String GENERATED_BY = """
 // Generated by dart2js, the Dart to JavaScript compiler.
 """;
 const String HOOKS_API_USAGE = """
 // The code supports the following hooks:
 // dartPrint(message)   - if this function is defined it is called
 //                        instead of the Dart [print] method.
 // dartMainRunner(main) - if this function is defined, the Dart [main]
 //                        method will not be invoked directly.
 //                        Instead, a closure that will invoke [main] is
 //                        passed to [dartMainRunner].
 """;