[layoutng] LayoutOpportunities() only needs a bool, not an enum

The "avoid" argument only needs to distinguish between block and
inline/BFC, so simplify the argument list.

R=ikilpatrick@chromium.org,eae@chromium.org
BUG=635619

Review-Url: https://codereview.chromium.org/2264273003
Cr-Commit-Position: refs/heads/master@{#413607}
2 files changed