CSSOM already exposes fontDisplay property (behind the experimental flag).

We need to add the 'display' property to FontFace.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ec812adbe02d56c9efafcaa77c7dfd9121510959

commit ec812adbe02d56c9efafcaa77c7dfd9121510959
Author: ksakamoto <ksakamoto@chromium.org>
Date: Thu Jan 19 03:04:59 2017

CSS font-display: expose display property on FontFace

This adds "display" attribute to FontFace interface that reflects the
font-display value of corresponding @font-face CSS rule. Also, this adds
"display" field to FontFaceDescriptors dictionary, to make it possible
to construct a FontFace with specified font-display value. These
are still protected behind the experimental features flag.

This matches Firefox's experimental implementation.

Spec discussion: https://github.com/tabatkins/specs/issues/54

BUG= 682115 

Review-Url: https://codereview.chromium.org/2640753002
Cr-Commit-Position: refs/heads/master@{#444617}

[modify] https://crrev.com/ec812adbe02d56c9efafcaa77c7dfd9121510959/third_party/WebKit/LayoutTests/fast/css/fontface-properties-expected.txt
[modify] https://crrev.com/ec812adbe02d56c9efafcaa77c7dfd9121510959/third_party/WebKit/LayoutTests/fast/css/fontface-properties.html
[modify] https://crrev.com/ec812adbe02d56c9efafcaa77c7dfd9121510959/third_party/WebKit/LayoutTests/webexposed/global-interface-listing-expected.txt
[modify] https://crrev.com/ec812adbe02d56c9efafcaa77c7dfd9121510959/third_party/WebKit/Source/core/css/FontFace.cpp
[modify] https://crrev.com/ec812adbe02d56c9efafcaa77c7dfd9121510959/third_party/WebKit/Source/core/css/FontFace.h
[modify] https://crrev.com/ec812adbe02d56c9efafcaa77c7dfd9121510959/third_party/WebKit/Source/core/css/FontFace.idl
[modify] https://crrev.com/ec812adbe02d56c9efafcaa77c7dfd9121510959/third_party/WebKit/Source/core/css/FontFaceDescriptors.idl