Add --enable-slimming-paint command line flag

Add --enable-slimming-paint command line flag

Enables the slimming paint work: http://www.chromium.org/blink/slimming-paint
This is dependent on https://codereview.chromium.org/684653002/

Committed: https://crrev.com/b6fdf887332060c442dd131b90d1f0fee824b131
Cr-Commit-Position: refs/heads/master@{#301659}

[leviw_travelin_and_unemployed, 2014-10-27 22:26:27]

leviw@chromium.org changed reviewers:
+ jam@chromium.org, sievers@chromium.org

[no sievers, 2014-10-28 00:04:22]

lgtm

[leviw_travelin_and_unemployed, 2014-10-28 15:07:18]

The CQ bit was checked by leviw@chromium.org

[commit-bot: I haz the power, 2014-10-28 15:08:38]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/678763007/20001

[commit-bot: I haz the power, 2014-10-28 15:13:41]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-10-28 15:13:42]

Try jobs failed on following builders:
  chromium_presubmit on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/chromium_presub...)

[leviw_travelin_and_unemployed, 2014-10-28 16:41:45]

leviw@chromium.org changed reviewers:
+ inferno@chromium.org, palmer@chromium.org, wfh@chromium.org

[leviw_travelin_and_unemployed, 2014-10-28 16:41:46]

Can I get a review for content/public/common/common_param_traits_macros.h?

[Will Harris, 2014-10-28 16:46:24]

On 2014/10/28 16:41:46, leviw wrote:
> Can I get a review for content/public/common/common_param_traits_macros.h?

content/public/common/common_param_traits_macros.h lgtm

[leviw_travelin_and_unemployed, 2014-10-28 17:17:24]

The CQ bit was checked by leviw@chromium.org

[commit-bot: I haz the power, 2014-10-28 17:18:48]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/678763007/20001

[commit-bot: I haz the power, 2014-10-28 17:47:05]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2014-10-28 17:47:48]

Patchset 2 (id:??) landed as
https://crrev.com/b6fdf887332060c442dd131b90d1f0fee824b131
Cr-Commit-Position: refs/heads/master@{#301659}