[Font Load Events] Implement FontFaceSet methods

LayoutTests/fast/css/fontloader-loadingdone.html

Index: LayoutTests/fast/css/fontloader-loadingdone.html
diff --git a/LayoutTests/fast/css/fontloader-loadingdone.html b/LayoutTests/fast/css/fontloader-loadingdone.html
index a23ef5ec7fe48bf250db53b47a5c2d7598983006..12827b7128ba932439e9b80563012b8e8eb594e2 100644
--- a/LayoutTests/fast/css/fontloader-loadingdone.html
+++ b/LayoutTests/fast/css/fontloader-loadingdone.html
@@ -28,8 +28,8 @@ function runTests() {
         shouldBeEqualToString('window.getComputedStyle(testDiv, 0).width', '48px');
     };
 
-    document.fonts.notifyWhenFontsReady(function() {
-        debug('notifyWhenFontsReady() callback');
+    document.fonts.ready().then(function() {
+        debug('ready() promise fulfilled');
         shouldBeEqualToString('window.getComputedStyle(testDiv, 0).width', '48px');
         finishJSTest();
     });