DisplayTopology: user cannot drag only display

When dragging a single display, we don't constrain the position of the
display, and the user can drag it anywhere on the fragment. As such we
need to either prevent the drag or refresh the pane always if there is
only one display. This CL chooses the former.

Flag: com.android.settings.flags.display_topology_pane_in_display_list
Test: atest DisplayTopologyPreferenceTest.kt
Bug: b/352650922
Change-Id: Icb101b734ce9b88435f64a71bf77f878f9b230e0

tests/robotests/src/com/android/settings/connecteddevice/display/DisplayTopologyPreferenceTest.kt

@@ -102,6 +102,15 @@ class DisplayTopologyPreferenceTest {
                 .map { preference.mPaneContent.getChildAt(it) as DisplayBlock }
                 .toList()
 
+    fun singleDisplayTopology(): DisplayTopology {
+        val primaryId = 22;
+
+        val root = DisplayTopology.TreeNode(
+                primaryId, /* width= */ 200f, /* height= */ 160f, POSITION_LEFT, /* offset= */ 0f)
+
+        return DisplayTopology(root, primaryId)
+    }
+
     fun twoDisplayTopology(childPosition: Int, childOffset: Float): DisplayTopology {
         val primaryId = 1
 
@@ -287,6 +296,36 @@ class DisplayTopologyPreferenceTest {
         assertThat(preference.mTimesReceivedSameTopology).isEqualTo(1)
     }
 
+    @Test
+    fun cannotMoveSingleDisplay() {
+        injector.topology = singleDisplayTopology()
+        preparePane()
+
+        val paneChildren = getPaneChildren()
+        assertThat(paneChildren).hasSize(1)
+        val block = paneChildren[0]
+
+        val origY = block.unpaddedY
+
+        block.dispatchTouchEvent(MotionEventBuilder.newBuilder()
+                .setAction(MotionEvent.ACTION_DOWN)
+                .setPointer(0f, 0f)
+                .build())
+        block.dispatchTouchEvent(MotionEventBuilder.newBuilder()
+                .setAction(MotionEvent.ACTION_MOVE)
+                .setPointer(0f, 30f)
+                .build())
+
+        assertThat(block.unpaddedY).isWithin(0.01f).of(origY)
+
+        block.dispatchTouchEvent(MotionEventBuilder.newBuilder()
+                .setAction(MotionEvent.ACTION_UP)
+                .build())
+
+        // Block should be back to original position.
+        assertThat(block.unpaddedY).isWithin(0.01f).of(origY)
+    }
+
     @Test
     fun updatedTopologyCancelsDragIfNonTrivialChange() {
         val (leftBlock, rightBlock) = setupTwoDisplays(POSITION_LEFT, /* childOffset= */ 42f)