Fix dot() signature to avoid an implicit copy constructor call. That also fixes the build with Clang ToT compiler. BUG=chromium:681912 Change-Id: I1449ee0f1f3f031d64af1a1f64f43808d2a8a1b1 Reviewed-on: https://chromium-review.googlesource.com/428903 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org> Commit-Queue: Corentin Wallez <cwallez@chromium.org>