Enable video-rvfc by default

This CL turns on the HTMLVideoElement.requestVideoFrameCallback by
default.

I2S: https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/DcuNrnEQo4k
Spec: https://wicg.github.io/video-rvfc/
WPT: https://wpt.fyi/results/video-rvfc

Bug: 1012063
Change-Id: Ide74ef5cad0d7a9d77f3f0b64f5d446479136af1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2157966
Commit-Queue: Thomas Guilbert <tguilbert@chromium.org>
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#761068}

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -1458,7 +1458,7 @@
     {
       // See https://crbug.com/1012063
       name: "RequestVideoFrameCallback",
-      status: "experimental",
+      status: "stable",
     },
     {
       name: "ResizeObserverUpdates",

third_party/blink/web_tests/virtual/stable/webexposed/element-instance-property-listing-expected.txt

@@ -1101,6 +1101,7 @@ html element video
     property autoplay
     property buffered
     property canPlayType
+    property cancelVideoFrameCallback
     property captureStream
     property controls
     property controlsList
@@ -1136,6 +1137,7 @@ html element video
     property readyState
     property remote
     property requestPictureInPicture
+    property requestVideoFrameCallback
     property seekable
     property seeking
     property setMediaKeys

third_party/blink/web_tests/virtual/stable/webexposed/global-interface-listing-expected.txt

@@ -3689,9 +3689,11 @@ interface HTMLVideoElement : HTMLMediaElement
     getter webkitDroppedFrameCount
     getter webkitSupportsFullscreen
     getter width
+    method cancelVideoFrameCallback
     method constructor
     method getVideoPlaybackQuality
     method requestPictureInPicture
+    method requestVideoFrameCallback
     method webkitEnterFullScreen
     method webkitEnterFullscreen
     method webkitExitFullScreen