Add FontFaceSource interface and make it available on Document

third_party/WebKit/Source/core/css/FontFaceSource.idl

Index: third_party/WebKit/Source/core/css/FontFaceSource.idl
diff --git a/third_party/WebKit/Source/core/css/FontFaceSource.idl b/third_party/WebKit/Source/core/css/FontFaceSource.idl
new file mode 100644
index 0000000000000000000000000000000000000000..372bc36548f422b44482344702a90b5861c48106
--- /dev/null
+++ b/third_party/WebKit/Source/core/css/FontFaceSource.idl
@@ -0,0 +1,12 @@
+/*
+ * Copyright (C) 2017 Google Inc. All rights reserved.

[foolip, 2017/05/16 12:15:27]

Use the 3-line header that begins "Copyright 2017 The Chromium Authors."

[fserb, 2017/05/16 14:14:24]

I thought "cl format" or presubmit would pick this. Done.

+ */
+
+// https://dev.w3.org/csswg/css-font-loading/#font-face-source

[foolip, 2017/05/16 12:15:27]

Link to https://drafts.csswg.org/css-font-loading/#font-face-source

[fserb, 2017/05/16 14:14:24]

Done.

+
+[
+  LegacyTreatAsPartialInterface,
+  NoInterfaceObject
+] interface FontFaceSource {
+  [MeasureAs=DocumentFonts] readonly attribute FontFaceSet fonts;
+};