Rename IntRectExtent to IntBoxExtent

Rename IntRectExtent to IntBoxExtent

Rename the IntRectExtent class to IntBoxExtent to match the naming of
the LayoutUnit and floating point versions of the same concept.

R=leviw@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=169675

[leviw_travelin_and_unemployed, 2014-03-20 18:02:33]

Okay. LGTM.

[eae, 2014-03-20 18:05:48]

The CQ bit was checked by eae@chromium.org

[commit-bot: I haz the power, 2014-03-20 18:05:49]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/eae@chromium.org/206373006/1

[commit-bot: I haz the power, 2014-03-20 18:11:48]

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

[commit-bot: I haz the power, 2014-03-20 18:11:48]

Try jobs failed on following builders:
  tryserver.blink on linux_blink_rel

[eae, 2014-03-20 18:14:27]

The CQ bit was checked by eae@chromium.org

[commit-bot: I haz the power, 2014-03-20 18:14:36]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/eae@chromium.org/206373006/1

[commit-bot: I haz the power, 2014-03-20 19:00:48]

Change committed as 169675