Fix spurious errors when dragging Web Inspector elements

webkit/glue/devtools/js/devtools.js

 // Copyright (c) 2009 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /**
  * @fileoverview Tools is a main class that wires all components of the
  * DevTools frontend together. It is also responsible for overriding existing
  * WebInspector functionality while it is getting upstreamed into WebCore.
  */
 goog.provide('devtools.Tools');
@@ skipping 320 matching lines @@
     }
     return result;
   };
 })();
 
 
 /** Pending WebKit upstream by apavlov). Fixes iframe vs drag problem. */
 (function() {
   var originalDragStart = WebInspector.elementDragStart;
   WebInspector.elementDragStart = function(element) {
-    var glassPane = document.createElement("div");
-    glassPane.style.cssText =
-        'position:absolute;width:100%;height:100%;opacity:0;z-index:1';
-    glassPane.id = 'glass-pane-for-drag';
-    element.parentElement.appendChild(glassPane);
+    if (element) {
+      var glassPane = document.createElement("div");
+      glassPane.style.cssText =
+          'position:absolute;width:100%;height:100%;opacity:0;z-index:1';
+      glassPane.id = 'glass-pane-for-drag';
+      element.parentElement.appendChild(glassPane);
+    }
 
     originalDragStart.apply(this, arguments);
   };
 
   var originalDragEnd = WebInspector.elementDragEnd;
   WebInspector.elementDragEnd = function() {
     originalDragEnd.apply(this, arguments);
 
     var glassPane = document.getElementById('glass-pane-for-drag');
-    glassPane.parentElement.removeChild(glassPane);
+    if (glassPane) {
+      glassPane.parentElement.removeChild(glassPane);
+    }
   };
 })();
 
 
 (function () {
 var orig = InjectedScriptAccess.getProperties;
 InjectedScriptAccess.getProperties = function(
     objectProxy, ignoreHasOwnProperty, callback) {
   if (objectProxy.isScope) {
     devtools.tools.getDebuggerAgent().resolveScope(objectProxy.objectId,
@@ skipping 79 matching lines @@
     includeInspectorCommandLineAPI, callFrameId, reportCompletions) {
   if (goog.isDef(callFrameId)) {
     devtools.tools.getDebuggerAgent().resolveCompletionsOnFrame(
         expressionString, callFrameId, reportCompletions);
   } else {
     return orig.apply(this, arguments);
   }
 };
 })();