Add stacktrace_test

pkg/compiler/lib/src/io/position_information.dart

Index: pkg/compiler/lib/src/io/position_information.dart
diff --git a/pkg/compiler/lib/src/io/position_information.dart b/pkg/compiler/lib/src/io/position_information.dart
index b4a764fc53b09cbef9eca8cd050a2030db2cb569..cfb6657aea7e777ac563509e50eb70c664c00663 100644
--- a/pkg/compiler/lib/src/io/position_information.dart
+++ b/pkg/compiler/lib/src/io/position_information.dart
@@ -522,7 +522,7 @@ class PositionTraceListener extends TraceListener
   void onStep(js.Node node, Offset offset, StepKind kind) {
     SourceInformation sourceInformation = computeSourceInformation(node);
     if (sourceInformation == null) return;
-    int codeLocation = offset.subexpressionOffset;
+    int codeLocation = offset.value;
     if (codeLocation == null) return;
 
     void registerPosition(SourcePositionKind sourcePositionKind) {
@@ -676,6 +676,8 @@ class Offset {
   Offset(
       this.statementOffset, this.leftToRightOffset, this.subexpressionOffset);
 
+  int get value => subexpressionOffset;
+
   String toString() {
     return 'Offset[statementOffset=$statementOffset,'
         'leftToRightOffset=$leftToRightOffset,'