Backed out changeset 295944fe65f9 (bug 1068400) for causing dt4 leaks

toolkit/devtools/server/actors/childtab.js

@@ -29,17 +29,20 @@ function ContentActor(connection, chromeGlobal)
   this.traits.reconfigure = false;
   this._sendForm = this._sendForm.bind(this);
   this._chromeGlobal.addMessageListener("debug:form", this._sendForm);
-
-  Object.defineProperty(this, "docShell", {
-    value: this._chromeGlobal.docShell,
-    configurable: true
-  });
 }
 
 ContentActor.prototype = Object.create(TabActor.prototype);
 
 ContentActor.prototype.constructor = ContentActor;
 
+Object.defineProperty(ContentActor.prototype, "docShell", {
+  get: function() {
+    return this._chromeGlobal.docShell;
+  },
+  enumerable: true,
+  configurable: true
+});
+
 Object.defineProperty(ContentActor.prototype, "title", {
   get: function() {
     return this.window.document.title;

toolkit/devtools/server/actors/webbrowser.js

@@ -1626,17 +1626,24 @@ function BrowserTabActor(aConnection, aBrowser, aTabBrowser)
   TabActor.call(this, aConnection, aBrowser);
   this._browser = aBrowser;
   this._tabbrowser = aTabBrowser;
-
-  Object.defineProperty(this, "docShell", {
-    value: this._browser.docShell,
-    configurable: true
-  });
 }
 
 BrowserTabActor.prototype = Object.create(TabActor.prototype);
 
 BrowserTabActor.prototype.constructor = BrowserTabActor;
 
+Object.defineProperty(BrowserTabActor.prototype, "docShell", {
+  get: function() {
+    if (this._browser) {
+      return this._browser.docShell;
+    }
+    // The tab is closed.
+    return null;
+  },
+  enumerable: true,
+  configurable: true
+});
+
 Object.defineProperty(BrowserTabActor.prototype, "title", {
   get: function() {
     // On Fennec, we can check the session store data for zombie tabs