Remove obsolete WebVector::IsEmpty().

BUG=none

Change-Id: If8781725a059b835cd48796e4ccb93244244e59a
Reviewed-on: https://chromium-review.googlesource.com/c/1482145
Commit-Queue: Scott Violet <sky@chromium.org>
Auto-Submit: Avi Drissman <avi@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634695}
13 files changed