Bug 681718 - Fix JS errors from text selection when long-tapping on local pages [r=mfinkle]

mobile/chrome/content/content.js

@@ -1365,7 +1365,7 @@ var SelectionHandler = {
       elem = utils.elementFromPoint(x, y, true, false);
     }
     if (!elem)
-      return;
+      return {};
     
     return { contentWindow: elem.ownerDocument.defaultView, offset: offset };
   },
@@ -1384,6 +1384,9 @@ var SelectionHandler = {
         let x = json.x - scrollOffset.x;
         let y = json.y - scrollOffset.y;
         let { contentWindow: contentWindow, offset: offset } = this.getCurrentWindowAndOffset(x, y, scrollOffset);
+        if (!contentWindow)
+          return;
+
         let currentDocShell = contentWindow.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIWebNavigation).QueryInterface(Ci.nsIDocShell);
 
         // Remove any previous selected or created ranges. Tapping anywhere on a
@@ -1498,6 +1501,9 @@ var SelectionHandler = {
         this.cache.rect = this._extractFromRange(range, this.cache.offset).rect;
         break;
       case "Browser:SelectionMeasure": {
+        if (!this.contentWindow)
+          return;
+
         let selection = this.contentWindow.getSelection();
         let range = selection.getRangeAt(0).QueryInterface(Ci.nsIDOMNSRange);
         if (!range)