Add source location to function declarations.

tests/compiler/dart2js/sourcemaps/js_tracer.dart

 // Copyright (c) 2016, 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 sourcemap.js_tracer;
 
 import 'package:compiler/src/io/source_information.dart';
 import 'package:compiler/src/io/position_information.dart';
 import 'package:compiler/src/js/js.dart' as js;
 import 'sourcemap_helper.dart';
@@ skipping 17 matching lines @@
   final TraceGraph graph;
 
   StepTraceListener(this.graph);
 
   @override
   void onStep(js.Node node, Offset offset, StepKind kind) {
     SourceInformation sourceInformation = computeSourceInformation(node);
     SourcePositionKind sourcePositionKind = SourcePositionKind.START;
     List text = [node];
     switch (kind) {
-      case StepKind.FUN:
+      case StepKind.FUN_ENTRY:
+        text = ['<entry>'];
+        break;
+      case StepKind.FUN_EXIT:
         sourcePositionKind = SourcePositionKind.INNER;
         text = ['<exit>'];
         break;
       case StepKind.CALL:
         CallPosition callPosition =
             CallPosition.getSemanticPositionForCall(node);
         sourcePositionKind = callPosition.sourcePositionKind;
         break;
       case StepKind.NEW:
       case StepKind.RETURN:
@@ skipping 86 matching lines @@
         branch = '$value';
         break;
     }
     graph.pushBranch(branch);
   }
 
   void popBranch() {
     graph.popBranch();
   }
 }