Let autorebaseliner to its work.

Turn NeedsManualRebaseline to NeedsRebaseline now that
all the pieces of resizing plumbing have landed.

BUG=309760
TBR=jochen

Review URL: https://codereview.chromium.org/70593002

git-svn-id: svn://svn.chromium.org/blink/trunk@161841 bbb929c8-8fbe-4397-9dbb-9b2b20218538