New media playback UI.

LayoutTests/media/video-controls-hidden-audio.html

+<video controls></video>
+<p>Test that hiding volume / mute buttons works as expected.</p>
+<script src=media-file.js></script>
+<script src=video-test.js></script>
+<script src=media-controls.js></script>
+<script>
+    // Enable hidden audio mode.
+    run("window.internals.settings.setForceAllowHiddenAudioElements(true)");
+
+    // Request non-hidden audio
+    run("window.internals.settings.setPreferHiddenVolumeSlider(false)");
+    run("window.internals.settings.setPreferHiddenMuteButton(false)");
+
+    // Starting with unmuted video, 
+    video.src = findMediaFile("video", "content/test");
+    run("video.load()");
+    waitForEvent("canplaythrough", function () {
+        muteButton = mediaControlsButton(video, "mute-button");
+        volumeSlider = mediaControlsButton(video, "volume-slider");
+
+        // Make sure that both are visible.
+        testExpected("getComputedStyle(muteButton).display", "none", '!=');
+        testExpected("getComputedStyle(volumeSlider).display", "none", '!=');
+
+        // Switch to muted video.  Both should still be visible.
+        run("video.muted = true");
+        testExpected("getComputedStyle(muteButton).display", "none", '!=');
+        testExpected("getComputedStyle(volumeSlider).display", "none", '!=');
+
+        // Prefer hidden audio.
+        run("window.internals.settings.setPreferHiddenVolumeSlider(true)");
+        run("window.internals.settings.setPreferHiddenMuteButton(true)");
+
+        // Switch back to unmuted video.  Both should now hide.
+        run("video.muted = false");  // So that it notices new settings!
+        testExpected("getComputedStyle(muteButton).display", "none", '==');
+        testExpected("getComputedStyle(volumeSlider).display", "none", '==');
+
+        // For muted video, the volume slider will hide but the mute
+        // button should come back, to let the user unmute.
+        run("video.muted = true");
+        testExpected("getComputedStyle(muteButton).display", "none", '!=');
+        testExpected("getComputedStyle(volumeSlider).display", "none", '==');
+
+        endTest();
+    });
+</script>