The reason is that non-configurability still allows a writable property to become read-only. BUG=chromium:663750 Review-Url: https://codereview.chromium.org/2508873002 Cr-Commit-Position: refs/heads/master@{#41029}
BUG=chromium:663750, chromium:664123 Review-Url: https://codereview.chromium.org/2495563002 Cr-Commit-Position: refs/heads/master@{#40902}
BUG=chromium:663750 Review-Url: https://codereview.chromium.org/2488223002 Cr-Commit-Position: refs/heads/master@{#40882}