Observatory improvements for exploring compiled code.

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

Index: runtime/observatory/lib/src/elements/script_inset.dart
diff --git a/runtime/observatory/lib/src/elements/script_inset.dart b/runtime/observatory/lib/src/elements/script_inset.dart
index 791534fdfbd3e32b4221cc08ffe260251626827e..66b125caa62926df5f17d04278a80a9b723f9f9f 100644
--- a/runtime/observatory/lib/src/elements/script_inset.dart
+++ b/runtime/observatory/lib/src/elements/script_inset.dart
@@ -439,8 +439,12 @@ class ScriptInsetElement extends ObservatoryElement {
                     ? script.tokenToLine(currentPos)
                     : null);
     _currentCol = (currentPos != null
-                   ? (script.tokenToCol(currentPos) - 1)  // make this 0-based.
+                   ? (script.tokenToCol(currentPos))
                    : null);
+    if (_currentCol != null) {
+      _currentCol--;  // make this 0-based.
+    }
+
     _endLine = (endPos != null
                 ? script.tokenToLine(endPos)
                 : script.lines.length + script.lineOffset);
@@ -564,6 +568,10 @@ class ScriptInsetElement extends ObservatoryElement {
     var table = new DivElement();
     table.classes.add("sourceTable");
 
+    if (_startLine == null || _endLine == null) {
+      return table;
+    }
+
     annotationsCursor = 0;
 
     int blankLineCount = 0;