Add a UMA histogram for type of web font usage

Add a UMA histogram for type of web font usage

This patch adds WebFont.PackageFormat histogram that tracks the usage of
different format of web fonts. It records container format of font file;
both TrueType fonts and OpenType fonts are recorded as SFNT format.
If a font didn't pass OTS sanitization, it's recoreded as Unknown.

BUG=380988
TEST=manually tested with chrome://histograms

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=175991

[bashi, 2014-06-10 08:35:39]

On 2014/06/10 06:31:12, Kunihiko Sakamoto wrote:

Non-owner LGTM.

[dglazkov, 2014-06-10 15:26:22]

lgtm

[Kunihiko Sakamoto, 2014-06-11 02:34:02]

The CQ bit was checked by ksakamoto@chromium.org

[commit-bot: I haz the power, 2014-06-11 02:34:43]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/ksakamoto@chromium.org/324003002/1

[commit-bot: I haz the power, 2014-06-11 03:44:01]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  win_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/11534)

[commit-bot: I haz the power, 2014-06-11 04:27:17]

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

[commit-bot: I haz the power, 2014-06-11 04:27:18]

Try jobs failed on following builders:
  win_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/11542)

[Kunihiko Sakamoto, 2014-06-12 01:39:09]

The CQ bit was checked by ksakamoto@chromium.org

[commit-bot: I haz the power, 2014-06-12 01:39:39]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/ksakamoto@chromium.org/324003002/20001

[commit-bot: I haz the power, 2014-06-12 05:43:25]

Change committed as 175991