Add ability to set the border insets of a box layout.

Add ability to set the border insets of a box layout.

This CL makes it possible to give a border insets to box layout which
overrides the constructor settings for border spacing. This lets the
client have more control on the insets of its child views.

This is a precursor to https://codereview.chromium.org/307333002/.

BUG=349727
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=275295

[calamity, 2014-06-04 05:15:01]

+sadrul for ui/views OWNERS.

[sadrul, 2014-06-04 22:39:20]

lgtm

[calamity, 2014-06-05 01:19:31]

The CQ bit was checked by calamity@chromium.org

[commit-bot: I haz the power, 2014-06-05 01:21:15]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/calamity@chromium.org/310753002/1

[commit-bot: I haz the power, 2014-06-05 06:09:31]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  android_chromium_gn_compile_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/android_chromium_gn_c...)
  linux_chromium_gn_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/linux_chromium_gn_rel...)

[commit-bot: I haz the power, 2014-06-05 06:15:08]

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

[commit-bot: I haz the power, 2014-06-05 06:15:09]

Try jobs failed on following builders:
  android_chromium_gn_compile_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/android_chromium_gn_c...)

[calamity, 2014-06-06 01:14:37]

The CQ bit was checked by calamity@chromium.org

[commit-bot: I haz the power, 2014-06-06 01:16:25]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/calamity@chromium.org/310753002/1

[commit-bot: I haz the power, 2014-06-06 01:39:38]

Change committed as 275295