It seems the issue here is that there are two situations that are no longer handled by the code grabbing the drawable size:
1. When the drawable is null.
2. When the drawable is in fact a GdkPixmap.
For the time being this diables the sanity check for WebKit2, but we can wait to add support for that when we decide whether or not to drop GTK+ 2.x support for WebKit2.
Created attachment 92019 [details]
Style bot: We have to keep the parameter name because this header is used in C code.
Attachment 92019 [details] did not pass style-queue:
Failed to run "['Tools/Scripts/check-webkit-style', '--diff-files', u'Source/WebCore/ChangeLog', u'Source/WebCor..." exit_code: 1
Source/WebCore/platform/gtk/GtkVersioning.h:38: The parameter name "drawable" adds no information, so it should be removed. [readability/parameter_name] 
Total errors found: 1 in 4 files
If any of these errors are false positives, please file a bug against check-webkit-style.
Comment on attachment 92019 [details]
View in context: https://bugs.webkit.org/attachment.cgi?id=92019&action=review
> + g_assert(GDK_IS_PIXMAP(drawable) || GDK_IS_WINDOW(drawable));
This will crash in release builds, so better change it for g_return_if_fail.
Committed r86178: <http://trac.webkit.org/changeset/86178>