Add parseFontFaceDescriptor for @font-face handling

Source/core/css/FontFace.cpp

Index: Source/core/css/FontFace.cpp
diff --git a/Source/core/css/FontFace.cpp b/Source/core/css/FontFace.cpp
index 1a251730b35858aa4876e7655cedf46d1544635b..f61d991f688da6bb5e7cee5c0d78a0c278d9d42f 100644
--- a/Source/core/css/FontFace.cpp
+++ b/Source/core/css/FontFace.cpp
@@ -65,7 +65,16 @@ namespace blink {
 static PassRefPtrWillBeRawPtr<CSSValue> parseCSSValue(const Document* document, const String& s, CSSPropertyID propertyID)
 {
     CSSParserContext context(*document, UseCounter::getFrom(document));
-    return CSSParser::parseSingleValue(propertyID, s, context);
+    StringBuilder builder;
+    builder.appendLiteral("@font-face { ");
+    builder.append(getPropertyNameString(propertyID));
+    builder.appendLiteral(" : ");
+    builder.append(s);
+    builder.appendLiteral("; }");
+    RefPtrWillBeRawPtr<StyleRuleBase> rule = CSSParser::parseRule(context, 0, builder.toString());
+    if (!rule || !rule->isFontFaceRule())
+        return nullptr;
+    return toStyleRuleFontFace(rule.get())->properties().getPropertyCSSValue(propertyID);
 }
 
 PassRefPtrWillBeRawPtr<FontFace> FontFace::create(ExecutionContext* context, const AtomicString& family, StringOrArrayBufferOrArrayBufferView& source, const FontFaceDescriptors& descriptors)