This changes the inlining candidates to be stored in a sorted set of
unique entries instead of a vector. We can avoid the final sorting
operation by amortizing the cost across insertions and also duplicate
entries are not created in the first place. Duplicate entries cause
crashes when candidates are processed.

R=bmeurer@chromium.org
BUG=chromium:549113
LOG=n

Review URL: https://codereview.chromium.org/1430553003

Cr-Commit-Position: refs/heads/master@{#31742}