This runs the existing checkpoint elimination during the "inlining"
optimization phase. It will eliminate redundant checkpoint nodes and
hence reduce graph size earlier. After this change the reducer in
question runs during {InliningPhase} as well as {TypedLoweringPhase}.

R=bmeurer@chromium.org

Review-Url: https://codereview.chromium.org/2670763003
Cr-Commit-Position: refs/heads/master@{#42918}