Invalidate clipPath clients after mutating 'transform'

When the 'transform' presentation attribute (or CSS property) was
mutated on a <clipPath>, its clients were not notified. Make sure they
are.

Bug: 881700
Change-Id: Id42aedf814472d8156804a955e6bbf2aa2792ec2
Reviewed-on: https://chromium-review.googlesource.com/1213142
Reviewed-by: Stephen Chenney <schenney@chromium.org>
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#589511}
7 files changed