Fixed stack trace for isolates without any Dart frames.

runtime/bin/vmstats/isolate_list.dart

Index: runtime/bin/vmstats/isolate_list.dart
===================================================================
--- runtime/bin/vmstats/isolate_list.dart	(revision 21569)
+++ runtime/bin/vmstats/isolate_list.dart	(working copy)
@@ -17,6 +17,7 @@
   static const String NEW_SPACE = 'new_space';
   static const String OLD_SPACE = 'old_space';
   static const String STACK_FRAME = 'stack_frame';
+  static const String EMPTY_STACK_FRAME = 'empty_stack_frame';
   static const String STACK_LIMIT = 'stack_limit';
   static const String STACK_TRACE = 'stack_trace';
   static const String STACK_TRACE_TITLE = 'stack_trace_title';
@@ -58,7 +59,7 @@
         stacktrace.classes.addAll([STACK_TRACE, HIDDEN]);
         stacktraceCell.children.add(stacktrace);
 
-        isolateRow.onClick.listen((e) => toggle(isolateRow));
+        isolateRow.onClick.listen((e) => toggleRow(isolateRow));
         updateIsolateDetails(isolate, isolateRow);
       }
     }
@@ -73,20 +74,28 @@
     title.text = "Stack Trace";
     element.children.add(title);
 
-    var stackIterator = response['stacktrace'].iterator;
-    var i = 0;
-    while (stackIterator.moveNext()) {
-      i++;
-      var frame = stackIterator.current;
-      var frameElement = new DivElement();
-      frameElement.$dom_className = STACK_FRAME;
-      var text = '$i: ${frame["url"]}:${frame["line"]}: ${frame["function"]}';
-      var code = frame["code"];
-      if (code['optimized']) {
-        text = '$text (optimized)';
+    var stackTrace = response['stacktrace'];
+    if (stackTrace.length > 0) {
+      var stackIterator = response['stacktrace'].iterator;
+      var i = 0;
+      while (stackIterator.moveNext()) {
+        i++;
+        var frame = stackIterator.current;
+        var frameElement = new DivElement();
+        var text = '$i: ${frame["url"]}:${frame["line"]}: ${frame["function"]}';
+        var code = frame["code"];
+        if (code['optimized']) {
+          text = '$text (optimized)';
+        }
+        frameElement.text = text;
+        frameElement.$dom_className = STACK_FRAME;
+        element.children.add(frameElement);
       }
-      frameElement.text = text;
-      element.children.add(frameElement);
+    } else {
+      DivElement noStack = new DivElement();
+      noStack.$dom_className = EMPTY_STACK_FRAME;
+      noStack.text = "<no stack>";
+      element.children.add(noStack);
     }
   }
 
@@ -114,12 +123,13 @@
         (String response) => setStacktrace(stackTrace, response));
   }
 
-  void toggle(TableRowElement row) {
-    var details = row.query('.$DETAILS');
-    details.classes.toggle(VISIBLE);
-    details.classes.toggle(HIDDEN);
-    var stacktrace = row.query('.$ISOLATE_STACKTRACE_COLUMN');
-    stacktrace.classes.toggle(VISIBLE);
-    stacktrace.classes.toggle(HIDDEN);
+  void toggleRow(TableRowElement row) {
+    toggleElement(row.query('.$DETAILS'));
+    toggleElement(row.query('.$ISOLATE_STACKTRACE_COLUMN'));
   }
+
+  void toggleElement(Element e) {
+    e.classes.toggle(VISIBLE);
+    e.classes.toggle(HIDDEN);
+  }
 }