port 3cfcc7e1 (r36786)

  original commit message:
  It may be that we have a feedback vector, but no literals. In this case
  we can store into the OptimizedCodeMap directly instead of using a WeakCell,
  because all data in the feedback vector is already held weakly.

  The use of a WeakCell in the OptimizedCodeMap is only required when
  there are literals which may hold maps strongly.

  This is to address a performance regression caused by the creation of
  a large number of WeakCells.

BUG=

Review-Url: https://codereview.chromium.org/2081663004
Cr-Commit-Position: refs/heads/master@{#37123}