Debug evaluate no longer writes back changes to the replicated
context chain to the original after execution. Changes to the
global object or script contexts still stick. Calling functions
that bind to the original context chain also have their expected
side effects.

As far as I can tell, DevTools is not interested in modifying
local variable values. Modifying global variable values still
works as expected. However, I have not yet removed the old
implementation, but merely keep it behind a flag.

R=mstarzinger@chromium.org, rossberg@chromium.org

Committed: https://crrev.com/92caa9b85eefffbef51c67428397951bd2e2c330
Cr-Commit-Position: refs/heads/master@{#32841}

Review URL: https://codereview.chromium.org/1513183003

Cr-Commit-Position: refs/heads/master@{#32857}