Use font properties of @font-face for local font selection

Since a @font-face defines a single font face, not a family, font
face selection for local() source of @font-face rules should be done
using the @font-face descriptors rather than the element style.

For example, if @font-face defines a normal face, always the normal
face should be used even if multiple faces (normal, bold, italic, etc.)
are installed on the system. If the element has "font-weight:bold;"
style, synthetic bold of the normal face should be used.
This behavior matches FireFox.

This patch realizes that behavior by updating FontDescription with
@font-face's descriptor values in CSSSegmentedFontFace::getFontData.
Also, makes FontCache::createFontPlatformData to use synthetic
bold/italic when the FontDescription specifies that.

BUG=120453
TEST=fast/css/font-face-synthetic-bold-italic-for-locally-installed.html

Review URL: https://codereview.chromium.org/82593003

git-svn-id: svn://svn.chromium.org/blink/trunk@162592 bbb929c8-8fbe-4397-9dbb-9b2b20218538