Ship OffscreenCanvas and Worker.requestAnimationFrame

Bug: 563816
Change-Id: I3939845a5c512f7a1975b2da7592595572cbc522
Reviewed-on: https://chromium-review.googlesource.com/1119156Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Reviewed-by: Justin Novosad <junov@chromium.org>
Commit-Queue: Fernando Serboncini <fserb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571657}

third_party/WebKit/LayoutTests/virtual/stable/webexposed/element-instance-property-listing-expected.txt

@@ -413,6 +413,7 @@ html element canvas
     property height
     property toBlob
     property toDataURL
+    property transferControlToOffscreen
     property width
 html element caption
     property align

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -847,11 +847,11 @@
     },
     {
       name: "OffscreenCanvas",
-      status: "experimental",
+      status: "stable",
     },
     {
       name: "OffscreenCanvasText",
-      status: "experimental",
+      status: "stable",
     },
     {
       name: "OnDeviceChange",