Base JavaScript code position computation on JavaScript tracer.

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

Index: pkg/compiler/lib/src/js/js_debug.dart
diff --git a/pkg/compiler/lib/src/js/js_debug.dart b/pkg/compiler/lib/src/js/js_debug.dart
index 43ec1309d03b492d2feecec4ad84de60f69c2a74..d1e6f093c3b69ad16eb75ca0718bde177d0a59a5 100644
--- a/pkg/compiler/lib/src/js/js_debug.dart
+++ b/pkg/compiler/lib/src/js/js_debug.dart
@@ -7,7 +7,12 @@
 library js.debug;
 
 import 'package:js_ast/js_ast.dart';
-import '../util/util.dart' show Indentation, Tagging;
+
+import '../io/code_output.dart' show
+    BufferedCodeOutput;
+import '../util/util.dart' show
+    Indentation,
+    Tagging;
 
 /// Unparse the JavaScript [node].
 String nodeToString(Node node) {
@@ -57,7 +62,8 @@ class DebugPrinter extends BaseVisitor with Indentation, Tagging<Node> {
 }
 
 /// Simple printing context that doesn't throw on errors.
-class LenientPrintingContext extends SimpleJavaScriptPrintingContext {
+class LenientPrintingContext extends SimpleJavaScriptPrintingContext
+    implements BufferedCodeOutput {
   @override
   void error(String message) {
     buffer.write('>>$message<<');