Better DDC sourcemap generation for lambdas

pkg/dev_compiler/lib/src/compiler/code_generator.dart

 // Copyright (c) 2015, 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.
 
 import 'dart:collection' show HashMap, HashSet;
 import 'dart:math' show min, max;
 
 import 'package:analyzer/analyzer.dart' hide ConstantEvaluator;
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 3427 matching lines @@
     var body = js.call('# == null ? null : #',
         [_visit(left), _emitSet(_stripNullAwareOp(node, left), right)]);
     return new JS.MetaLet(vars, [body]);
   }
 
   @override
   JS.Block visitExpressionFunctionBody(ExpressionFunctionBody node) {
     var savedFunction = _currentFunction;
     _currentFunction = node;
     var initArgs = _emitArgumentInitializers(node.parent);
-    var ret = new JS.Return(_visit(node.expression));
+    var ret = annotate(new JS.Return(_visit(node.expression)), node.expression);
     _currentFunction = savedFunction;
-    return new JS.Block(initArgs != null ? [initArgs, ret] : [ret]);
+    var _statements = initArgs != null ? [initArgs, ret] : [ret];
+    var block = annotate(new JS.Block(_statements), node);
+    return block;
   }
 
   @override
   JS.Block visitEmptyFunctionBody(EmptyFunctionBody node) => new JS.Block([]);
 
   @override
   JS.Block visitBlockFunctionBody(BlockFunctionBody node) {
     var savedFunction = _currentFunction;
     _currentFunction = node;
     var initArgs = _emitArgumentInitializers(node.parent);
@@ skipping 2487 matching lines @@
   if (targetIdentifier.staticElement is! PrefixElement) return false;
   var prefix = targetIdentifier.staticElement as PrefixElement;
 
   // The library the prefix is referring to must come from a deferred import.
   var containingLibrary = resolutionMap
       .elementDeclaredByCompilationUnit(target.root as CompilationUnit)
       .library;
   var imports = containingLibrary.getImportsWithPrefix(prefix);
   return imports.length == 1 && imports[0].isDeferred;
 }