Add about:flags support for doc.write script blocking.

This is a merge into M51 branch 2704.

Add about:flags support for doc.write script blocking.

This patch introduces an additional blink setting which allows us to enable
blocking only on slow (2G) connections, or on all connections.

This is consistent with the 2G web font intervention, which has a feature
for enabling on 2G, and an additional feature to force the intervention on
in all connection types.

We then add support for enabling the setting that enables blocking on all
connection types from about:flags.

This change also removes about:flags support from the now discontinued low
priority iframe experiment, since it's nontrivial to add support for
multiple blink settings in about:flags.

BUG=602137
TBR=japhet@chromium.org

Review URL: https://codereview.chromium.org/1868413002

Cr-Commit-Position: refs/heads/master@{#386769}
(cherry picked from commit ed75dc7053dc072bdd0e72f64a869d59ec587f4b)

Committed: https://chromium.googlesource.com/chromium/src/+/afcacf06e0bf288ec36b567c454b52764b681fed

[jkarlin, 2016-04-13 19:14:28]

Description was changed from

==========
Add about:flags support for doc.write script blocking.

This patch introduces an additional blink setting which allows us to enable
blocking only on slow (2G) connections, or on all connections.

This is consistent with the 2G web font intervention, which has a feature
for enabling on 2G, and an additional feature to force the intervention on
in all connection types.

We then add support for enabling the setting that enables blocking on all
connection types from about:flags.

This change also removes about:flags support from the now discontinued low
priority iframe experiment, since it's nontrivial to add support for
multiple blink settings in about:flags.

BUG=602137

Review URL: https://codereview.chromium.org/1868413002

Cr-Commit-Position: refs/heads/master@{#386769}
(cherry picked from commit ed75dc7053dc072bdd0e72f64a869d59ec587f4b)
==========

to

==========
This is a merge into M51 branch 2704.

Add about:flags support for doc.write script blocking.

This patch introduces an additional blink setting which allows us to enable
blocking only on slow (2G) connections, or on all connections.

This is consistent with the 2G web font intervention, which has a feature
for enabling on 2G, and an additional feature to force the intervention on
in all connection types.

We then add support for enabling the setting that enables blocking on all
connection types from about:flags.

This change also removes about:flags support from the now discontinued low
priority iframe experiment, since it's nontrivial to add support for
multiple blink settings in about:flags.

BUG=602137
TBR=japhet@chromium.org

Review URL: https://codereview.chromium.org/1868413002

Cr-Commit-Position: refs/heads/master@{#386769}
(cherry picked from commit ed75dc7053dc072bdd0e72f64a869d59ec587f4b)
==========

[jkarlin, 2016-04-13 19:18:08]

Description was changed from

==========
This is a merge into M51 branch 2704.

Add about:flags support for doc.write script blocking.

This patch introduces an additional blink setting which allows us to enable
blocking only on slow (2G) connections, or on all connections.

This is consistent with the 2G web font intervention, which has a feature
for enabling on 2G, and an additional feature to force the intervention on
in all connection types.

We then add support for enabling the setting that enables blocking on all
connection types from about:flags.

This change also removes about:flags support from the now discontinued low
priority iframe experiment, since it's nontrivial to add support for
multiple blink settings in about:flags.

BUG=602137
TBR=japhet@chromium.org

Review URL: https://codereview.chromium.org/1868413002

Cr-Commit-Position: refs/heads/master@{#386769}
(cherry picked from commit ed75dc7053dc072bdd0e72f64a869d59ec587f4b)
==========

to

==========
This is a merge into M51 branch 2704.

Add about:flags support for doc.write script blocking.

This patch introduces an additional blink setting which allows us to enable
blocking only on slow (2G) connections, or on all connections.

This is consistent with the 2G web font intervention, which has a feature
for enabling on 2G, and an additional feature to force the intervention on
in all connection types.

We then add support for enabling the setting that enables blocking on all
connection types from about:flags.

This change also removes about:flags support from the now discontinued low
priority iframe experiment, since it's nontrivial to add support for
multiple blink settings in about:flags.

BUG=602137
TBR=japhet@chromium.org

Review URL: https://codereview.chromium.org/1868413002

Cr-Commit-Position: refs/heads/master@{#386769}
(cherry picked from commit ed75dc7053dc072bdd0e72f64a869d59ec587f4b)

Committed:
https://chromium.googlesource.com/chromium/src/+/afcacf06e0bf288ec36b567c454b...
==========

[jkarlin, 2016-04-13 19:18:09]

Committed patchset #1 (id:1) manually as
afcacf06e0bf288ec36b567c454b52764b681fed (presubmit successful).