Port 662aa425

Original Commit Message:

    Since the feedback vector is itself a native context structure, why
    not store optimized code for a function in there rather than in
    a map from native context to code? This allows us to get rid of
    the optimized code map in the SharedFunctionInfo, saving a pointer,
    and making lookup of any optimized code quicker.

    Original patch by Michael Stanton <mvstanton@chromium.org>

R=rmcilroy@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=v8:6246
LOG=N

Review-Url: https://codereview.chromium.org/2861863003
Cr-Commit-Position: refs/heads/master@{#45111}