The previous patch for this bug (https://codereview.chromium.org/2599793002/) was wrong because it changed the behavior of isCreatedPhi() in an incompatible way. The actual source of the bug is that escape analysis propagates information along cycles without considering the previous analysis value. This fix makes sure that if a previous merge cleared a field, then it stays cleared.

R=bmeurer@chromium.org

BUG=chromium:670202

Review-Url: https://codereview.chromium.org/2610703002
Cr-Commit-Position: refs/heads/master@{#42045}