GCC: workaround error resolving IsA template in DeleteSelectionCommand

GCC fails to resolve IsA template as a function parameter in DeleteSelectionCommand.
To avoid this we add a static function that uses it internally, with the expected
function signature expected by EnclosingNodeOfType.

Bug: 819294
Change-Id: If9dfcfb4ca7e298d33545bfd870b6e3d05f9ce76
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2052173
Commit-Queue: José Dapena Paz <jdapena@igalia.com>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#743910}
1 file changed