Fix static analysis warnings in 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:async';
 import 'dart:html';
 import 'observatory_element.dart';
 import 'service_ref.dart';
@@ skipping 103 matching lines @@
     element.title = "Current execution";
   }
 }
 
 class BreakpointAnnotation extends Annotation {
   Breakpoint bpt;
   int priority = 1;
 
   BreakpointAnnotation(this.bpt) {
     var script = bpt.location.script;
-    if (bpt.location.tokenPos != null) {
-      var pos = bpt.location.tokenPos;
+    var location = bpt.location;
+    if (location.tokenPos != null) {
+      var pos = location.tokenPos;
       line = script.tokenToLine(pos);
       columnStart = script.tokenToCol(pos) - 1;  // tokenToCol is 1-origin.
-    } else {
-      line = bpt.location.line;
-      columnStart = bpt.location.column;
+    } else if (location is UnresolvedSourceLocation) {
+      line = location.line;
+      columnStart = location.column;
       if (columnStart == null) {
         columnStart = 0;
       }
     }
     var length = script.guessTokenLength(line, columnStart);
     if (length == null) {
       length = 1;
     }
     columnStop = columnStart + length;
   }
@@ skipping 871 matching lines @@
 @CustomTag('source-inset')
 class SourceInsetElement extends PolymerElement {
   SourceInsetElement.created() : super.created();
 
   @published SourceLocation location;
   @published String height = null;
   @published int currentPos;
   @published bool inDebuggerContext = false;
   @published ObservableList variables;
 }
-