Remove "transition-compositing" flags

Remove "transition-compositing" flags

This removes the "enable-transition-compositing" and
"disable-transition-compositing" flags and the corresponding
about:flags experiment. The feature controlled by these flags
was removed from Blink (in http://crrev.com/206593005), so
these flags are currently no-ops.

BUG=178119, 439845
Committed: https://crrev.com/efc4bbdd490026caf5e85ffc36af53219b1160aa
Cr-Commit-Position: refs/heads/master@{#307955}

[ajuma, 2014-12-11 16:44:14]

ajuma@chromium.org changed reviewers:
+ piman@chromium.org

[piman, 2014-12-11 18:17:17]

lgtm

[ajuma, 2014-12-11 18:25:19]

ajuma@chromium.org changed reviewers:
+ scottmg@chromium.org

[ajuma, 2014-12-11 18:26:25]

+scottmg for build/ OWNERS

[scottmg, 2014-12-11 18:50:09]

lgtm

[ajuma, 2014-12-11 18:55:43]

The CQ bit was checked by ajuma@chromium.org

[commit-bot: I haz the power, 2014-12-11 18:56:48]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/788393003/1

[commit-bot: I haz the power, 2014-12-11 19:58:43]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-12-11 19:59:46]

Patchset 1 (id:??) landed as
https://crrev.com/efc4bbdd490026caf5e85ffc36af53219b1160aa
Cr-Commit-Position: refs/heads/master@{#307955}