Bug 773980 - Don't touch dead objects in BrowserElementParent.js. r=mounir

dom/browser-element/BrowserElementParent.js

@@ -136,7 +136,12 @@ function BrowserElementParent(frameLoader) {
 
   let self = this;
   function addMessageListener(msg, handler) {
-    self._mm.addMessageListener('browser-element-api:' + msg, handler.bind(self));
+    function checkedHandler() {
+      if (self._isAlive()) {
+        handler.apply(self, arguments);
+      }
+    }
+    self._mm.addMessageListener('browser-element-api:' + msg, checkedHandler);
   }
 
   addMessageListener("hello", this._recvHello);
@@ -157,11 +162,19 @@ function BrowserElementParent(frameLoader) {
   addMessageListener('got-can-go-forward', this._gotDOMRequestResult);
 
   function defineMethod(name, fn) {
-    XPCNativeWrapper.unwrap(self._frameElement)[name] = fn.bind(self);
+    XPCNativeWrapper.unwrap(self._frameElement)[name] = function() {
+      if (self._isAlive()) {
+        return fn.apply(self, arguments);
+      }
+    };
   }
 
   function defineDOMRequestMethod(domName, msgName) {
-    XPCNativeWrapper.unwrap(self._frameElement)[domName] = self._sendDOMRequest.bind(self, msgName);
+    XPCNativeWrapper.unwrap(self._frameElement)[domName] = function() {
+      if (self._isAlive()) {
+        return self._sendDOMRequest(msgName);
+      }
+    };
   }
 
   // Define methods on the frame element.
@@ -176,6 +189,16 @@ function BrowserElementParent(frameLoader) {
 }
 
 BrowserElementParent.prototype = {
+  /**
+   * You shouldn't touch this._frameElement or this._window if _isAlive is
+   * false.  (You'll likely get an exception if you do.)
+   */
+  _isAlive: function() {
+    return !Cu.isDeadWrapper(this._frameElement) &&
+           !Cu.isDeadWrapper(this._frameElement.ownerDocument) &&
+           !Cu.isDeadWrapper(this._frameElement.ownerDocument.defaultView);
+  },
+
   get _window() {
     return this._frameElement.ownerDocument.defaultView;
   },