Remove custom style building for -webkit-font-feature-settings.

Remove custom style building for -webkit-font-feature-settings.

This patch replaces the custom style application for
-webkit-font-feature-settings with a function in StyleBuilderConverter.

Also:

 * Less use of CSSValue in FontBuilder.
 * We now handle 'initial' and 'inherit'.
 * Eliminates FontDescription::makeNormalFeatureSettings.

Note that in StyleBuilderConverter::convertFontFeatureSettings, the check
for isFontFeatureValue() is removed. Asserting (via toCSSFontFeatureValue)
should be enough, since the parser will only add CSSFontFeatureValues to the
list.

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=179764

[andersr, 2014-08-07 14:45:25]

Note: Based on: https://codereview.chromium.org/444413003/

[dglazkov, 2014-08-07 15:50:58]

lgtm

[andersr, 2014-08-07 21:23:45]

The CQ bit was checked by andersr@opera.com

[commit-bot: I haz the power, 2014-08-07 21:24:27]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/andersr@opera.com/444333005/1

[commit-bot: I haz the power, 2014-08-07 23:03:35]

Change committed as 179764