v8binding: Run content attributes injected by Extensions in the main world

Run script in content attributes that are injected by Chrome
extensions (content scripts) in the main world in order to keep
backward compatibility.

(cherry picked from commit 9aa69dc23c484b7364f446e0acebbb32f0f3e3f7)

Change-Id: Ie50d62e4a19c050dd2187638b383680bde492e2a
Bug: 912069
Reviewed-on: https://chromium-review.googlesource.com/c/1373283
Commit-Queue: Yuki Shiino <yukishiino@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#615860}
Reviewed-on: https://chromium-review.googlesource.com/c/1381361
Reviewed-by: Yuki Shiino <yukishiino@chromium.org>
Cr-Commit-Position: refs/branch-heads/3626@{#418}
Cr-Branched-From: d897fb137fbaaa9355c0c93124cc048824eb1e65-refs/heads/master@{#612437}
3 files changed