Don't attempt to show validation bubble for unparented web contents.

chrome/browser/ui/browser.cc

Index: chrome/browser/ui/browser.cc
diff --git a/chrome/browser/ui/browser.cc b/chrome/browser/ui/browser.cc
index 64ab742dcf3ab7a1e8945781e1bf59d60556fb78..d2bfd8f0f6e96aa03abf20857611e9ab76e95b98 100644
--- a/chrome/browser/ui/browser.cc
+++ b/chrome/browser/ui/browser.cc
@@ -1260,6 +1260,10 @@ void Browser::ShowValidationMessage(content::WebContents* web_contents,
                                     const gfx::Rect& anchor_in_root_view,
                                     const base::string16& main_text,
                                     const base::string16& sub_text) {
+  // If the web contents is unparented (e.g. in a blocked popup) it does not
+  // make sense to show a validation message. See http://crbug.com/616990
+  if (!web_contents->GetTopLevelNativeWindow())
+    return;
   validation_message_bubble_ =
       TabDialogs::FromWebContents(web_contents)
           ->ShowValidationMessage(anchor_in_root_view, main_text, sub_text);