port e0aa8ebf (r27103).

original commit message:

  This reduces the size of the StackHandler by one word. We no longer
  need to keep track of the code object, as the stack walk finds it.

BUG=
R=weiliang.lin@intel.com

Review URL: https://codereview.chromium.org/1022403002

Cr-Commit-Position: refs/heads/master@{#27353}