Debug-evaluate used to resolve stack variables that shadow
context variables incorrectly, since the stack variable is
not visible in the context chain.

To fix this, we limit local variables accessible by debug-
evaluate to the ones directly referenced inside the function.
What is not referenced by the function itself, is considered
optimized out and not accessible by debug-evaluate.

To achieve this, we duplicate the entire context chain up to
the native context, and write back changes after debug-
evaluate. Changes to the original context chain will however
be overwritten. This already happens for catch and block
scopes though.

Also fix a crash caused by declaring variables inside debug-
evaluate.

R=mstarzinger@chromium.org
BUG=v8:4593
LOG=N

Review URL: https://codereview.chromium.org/1500933002

Cr-Commit-Position: refs/heads/master@{#32828}