This CL is a workaround fix for a crash issue; to set "undefined" instead of deleting properties.

This CL is a workaround fix for a crash issue; to set "undefined" instead of deleting properties.

The root cause seems to be in V8 (http://crbug.com/v8/6227),
but Blink can avoid the crash with this workaround.
The workaround is not on spec, but it works for many cases and we
have used the behavior for a while.

BUG=709804
Review-Url: https://codereview.chromium.org/2812563002
Cr-Commit-Position: refs/heads/master@{#463227}
(cherry picked from commit 55f74b058ef1379b6c4bb527cee68c077729ab51)

Review-Url: https://codereview.chromium.org/2800393003 .
Cr-Commit-Position: refs/branch-heads/3067@{#3}
Cr-Branched-From: e2ed4b4539b7a50d8be892e4437897b18c181c91-refs/heads/master@{#463157}
Committed: https://chromium.googlesource.com/chromium/src/+/37f139a528deaf60c31762a68aa610c1935da904

[wkorman, 2017-04-10 19:43:11]

Description was changed from

==========
This CL is a workaround fix for a crash issue; to set "undefined" instead of
deleting properties.

The root cause seems to be in V8 (http://crbug.com/v8/6227),
but Blink can avoid the crash with this workaround.
The workaround is not on spec, but it works for many cases and we
have used the behavior for a while.

BUG=709804

Review-Url: https://codereview.chromium.org/2812563002
Cr-Commit-Position: refs/heads/master@{#463227}
(cherry picked from commit 55f74b058ef1379b6c4bb527cee68c077729ab51)
==========

to

==========
This CL is a workaround fix for a crash issue; to set "undefined" instead of
deleting properties.

The root cause seems to be in V8 (http://crbug.com/v8/6227),
but Blink can avoid the crash with this workaround.
The workaround is not on spec, but it works for many cases and we
have used the behavior for a while.

BUG=709804

Review-Url: https://codereview.chromium.org/2812563002
Cr-Commit-Position: refs/heads/master@{#463227}
(cherry picked from commit 55f74b058ef1379b6c4bb527cee68c077729ab51)

Review-Url: https://codereview.chromium.org/2800393003 .
Cr-Commit-Position: refs/branch-heads/3067@{#3}
Cr-Branched-From:
e2ed4b4539b7a50d8be892e4437897b18c181c91-refs/heads/master@{#463157}
Committed:
https://chromium.googlesource.com/chromium/src/+/37f139a528deaf60c31762a68aa6...
==========

[wkorman, 2017-04-10 19:43:12]

Committed patchset #1 (id:1) manually as
37f139a528deaf60c31762a68aa610c1935da904.