port d515e513(r31211).

contributed by zhengxing.li@intel.com

original commit message:
Previously, name conflicts between var and let declarations were only made into exceptions if they were visible at parse-time. This patch adds runtime checks so that sloppy-mode direct eval can't introduce conflicting var declarations. The change is implemented by traversing the scope chain when a direct eval introduces a var declaration to look for conflicting let declarations, up to the function boundary.

additional comment:
The original r31211 patch needs some additional changes for x87
1. Should use Smi::FromInt(variable->DeclarationPropertyAttributes())

BUG=

Review URL: https://codereview.chromium.org/1420683002

Cr-Commit-Position: refs/heads/master@{#31433}