Add a working command line debugger to Observatory.

runtime/observatory/lib/src/elements/script_inset.dart

 // Copyright (c) 2013, 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 script_inset_element;
 
 import 'dart:html';
 import 'observatory_element.dart';
 import 'package:observatory/service.dart';
 import 'package:polymer/polymer.dart';
 
 /// Box with script source code in it.
 @CustomTag('script-inset')
 class ScriptInsetElement extends ObservatoryElement {
   @published Script script;
 
   /// Set the height to make the script inset scroll.  Otherwise it
   /// will show from startPos to endPos.
   @published String height = null;
 
   @published int currentPos;
   @published int startPos;
   @published int endPos;
 
   @observable int currentLine;
+  @observable int currentCol;
   @observable int startLine;
   @observable int endLine;
   @observable bool linesReady = false;
 
   // Contents are either ScriptLine or ScriptElipsis.
   @observable List lines = toObservable([]);
 
   String makeLineId(int line) {
     return 'line-$line';
   }
 
+  String clip(String line, int start, [int limit]) {
+    try {
+      return line.substring(start, limit);
+    } catch (_) {
+      // NOTE(turnidge): Sometimes polymer updates give us garbage
+      // starts and limits during page updates.
+      return "OOB";
+    }
+  }
+
   MutationObserver _observer;
 
   void _scrollToCurrentPos() {
     var line = shadowRoot.querySelector('#line-$currentLine');
     if (line != null) {
       line.scrollIntoView();
     }
   }
 
   void _onMutation(mutations, observer) {
@@ skipping 54 matching lines @@
         }
       });
       return;
     }
     startLine = (startPos != null
                  ? script.tokenToLine(startPos)
                  : 1);
     currentLine = (currentPos != null
                    ? script.tokenToLine(currentPos)
                    : null);
+    currentCol = (currentPos != null
+                  ? (script.tokenToCol(currentPos) - 1)  // make this 0-based.
+                  : null);
     endLine = (endPos != null
                ? script.tokenToLine(endPos)
                : script.lines.length);
 
     lines.clear();
     int blankLineCount = 0;
     for (int i = (startLine - 1); i <= (endLine - 1); i++) {
       if (script.lines[i].isBlank) {
         // Try to introduce elipses if there are 4 or more contiguous blank lines.
         blankLineCount++;
@@ skipping 41 matching lines @@
     } else {
       // Existing breakpoint.  Remove it.
       line.script.isolate.removeBreakpoint(line.bpt).then((_) {
           busy = false;
       });
     }
   }
 
   BreakpointToggleElement.created() : super.created();
 }