[Media Controls] Fix cursor become pointer when hovering disabled controls.

Bug: 986231
Change-Id: I621b1309ad0920f57ca338ee607a518f2843263e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1731924Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Commit-Queue: Jazz Xu <jazzhsu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#683947}

third_party/blink/renderer/modules/media_controls/resources/mediaControls.css

@@ -385,6 +385,8 @@ video::-webkit-media-controls-play-button:disabled,
 video::-webkit-media-controls-fullscreen-button:disabled {
   background-color: initial;
   opacity: 0.3;
+
+  cursor: default;
 }
 
 audio::-internal-media-controls-cast-button,
@@ -623,6 +625,11 @@ video::-webkit-media-controls-timeline {
   box-sizing: unset !important;
 }
 
+audio::-webkit-media-controls-timeline:disabled,
+video::-webkit-media-controls-timeline:disabled {
+  cursor: default;
+}
+
 audio::-webkit-media-controls-timeline,
 video::-webkit-media-controls.audio-only [pseudo="-webkit-media-controls-timeline"] {
   padding-top: 26px;