[Media] Allow a11y interactions to change seekbar position.

Note that the seekbar UI can now get a bit janky if
you have TalkBack on and you very quickly swipe up or down. We can file
a new bug for that if we decide it needs fixing.

Fixes: 216254595
Fixes: 216254099
Test: SeekBarViewModelTest
Test: manual: Turn TalkBack on, select the seekbar, and verify you can
swipe up/down to change the track position.
Test: manual: Verify seeking without TalkBack on still works.

Change-Id: I890e4f396fa704047c5593fff20c8924b890fc75

packages/SystemUI/src/com/android/systemui/media/SeekBarViewModel.kt

@@ -151,13 +151,21 @@ class SeekBarViewModel @Inject constructor(
     }
 
     /**
-     * Event indicating that the user has moved the seek bar but hasn't yet finished the gesture.
+     * Event indicating that the user has moved the seek bar.
+     *
      * @param position Current location in the track.
      */
     @AnyThread
     fun onSeekProgress(position: Long) = bgExecutor.execute {
         if (scrubbing) {
+            // The user hasn't yet finished their touch gesture, so only update the data for visual
+            // feedback and don't update [controller] yet.
             _data = _data.copy(elapsedTime = position.toInt())
+        } else {
+            // The seek progress came from an a11y action and we should immediately update to the
+            // new position. (a11y actions to change the seekbar position don't trigger
+            // SeekBar.OnSeekBarChangeListener.onStartTrackingTouch or onStopTrackingTouch.)
+            onSeek(position)
         }
     }
 

packages/SystemUI/tests/src/com/android/systemui/media/SeekBarViewModelTest.kt

@@ -375,16 +375,20 @@ public class SeekBarViewModelTest : SysuiTestCase() {
     }
 
     @Test
-    fun onProgressChangedFromUserWithoutStartTrackingTouch() {
-        // WHEN user starts dragging the seek bar
+    fun onProgressChangedFromUserWithoutStartTrackingTouch_transportUpdated() {
+        whenever(mockController.transportControls).thenReturn(mockTransport)
+        viewModel.updateController(mockController)
         val pos = 42
         val bar = SeekBar(context)
+
+        // WHEN we get an onProgressChanged event without an onStartTrackingTouch event
         with(viewModel.seekBarListener) {
             onProgressChanged(bar, pos, true)
         }
         fakeExecutor.runAllReady()
-        // THEN then elapsed time should not be updated
-        assertThat(viewModel.progress.value!!.elapsedTime).isNull()
+
+        // THEN we immediately update the transport
+        verify(mockTransport).seekTo(pos.toLong())
     }
 
     @Test