Use ContentSize() for content size stored for paint invalidation

LayoutBox::ContentSize() is more to the point than calling
LayoutBox::ContentBoxRect() and then do Size() on the result (ignoring
the position.) Hopefully it is also faster (4 vs 8 virtual calls.)

Change-Id: If8c370446fad49d976d1d7576ac7041cd8d78180
Reviewed-on: https://chromium-review.googlesource.com/733164
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#510846}
2 files changed