Introduce elipses when there are long stretches of blank lines 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: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 startLine;
   @observable int endLine;
   @observable bool linesReady = false;
 
-  @observable List<ScriptLine> lines = toObservable([]);
+  // Contents are either ScriptLine or ScriptElipsis.
+  @observable List lines = toObservable([]);
 
   String makeLineId(int line) {
     return 'line-$line';
   }
 
   MutationObserver _observer;
 
   void _scrollToCurrentPos() {
     var line = shadowRoot.querySelector('#line-$currentLine');
     if (line != null) {
@@ skipping 64 matching lines @@
                  ? script.tokenToLine(startPos)
                  : 1);
     currentLine = (currentPos != null
                    ? script.tokenToLine(currentPos)
                    : null);
     endLine = (endPos != null
                ? script.tokenToLine(endPos)
                : script.lines.length);
 
     lines.clear();
+    int blankLineCount = 0;
     for (int i = (startLine - 1); i <= (endLine - 1); i++) {
-      lines.add(script.lines[i]);
+      if (script.lines[i].isBlank) {
+        // Try to introduce elipses if there are 4 or more contiguous blank lines.
+        blankLineCount++;
+      } else {
+        if (blankLineCount > 0) {
+          int firstBlank = i - blankLineCount;
+          int lastBlank = i - 1;
+          if (blankLineCount < 4) {
+            // Too few blank lines for an elipsis.
+            for (int j = firstBlank; j  <= lastBlank; j++) {
+              lines.add(script.lines[j]);
+            }
+          } else {
+            // Add an elipsis for the skipped region.
+            lines.add(script.lines[firstBlank]);
+            lines.add(null);
+            lines.add(script.lines[lastBlank]);
+          }
+          blankLineCount = 0;
+        }
+        lines.add(script.lines[i]);
+      }
     }
     linesReady = true;
   }
 
   ScriptInsetElement.created() : super.created();
 }
 
 @CustomTag('breakpoint-toggle')
 class BreakpointToggleElement extends ObservatoryElement {
   @published ScriptLine line;
@@ skipping 12 matching lines @@
     } else {
       // Existing breakpoint.  Remove it.
       line.script.isolate.clearBreakpoint(line.bpt).then((_) {
           busy = false;
       });
     }
   }
 
   BreakpointToggleElement.created() : super.created();
 }