Add funtional animation for SplitSelect from Grid.

Long ways to go to final UI - TODO(b/186800707)
Add comments to grid layout code,
no functional changes at all.

Bug: 181705607
Test: Enter split screen from overview task menu
in grid and carousel. Able to select all items
and enter split.

Change-Id: Ib62f1b286acf0781ec47862fa31b670e6ff1892a

src/com/android/launcher3/touch/PortraitPagedViewHandler.java

@@ -155,6 +155,25 @@ public class PortraitPagedViewHandler implements PagedOrientationHandler {
         return VIEW_TRANSLATE_Y;
     }
 
+    @Override
+    public int getSplitTaskViewDismissDirection(SplitPositionOption splitPosition,
+            DeviceProfile dp) {
+        if (splitPosition.mStagePosition == STAGE_POSITION_TOP_OR_LEFT) {
+            if (dp.isLandscape) {
+                // Left side
+                return SPLIT_TRANSLATE_PRIMARY_NEGATIVE;
+            } else {
+                // Top side
+                return SPLIT_TRANSLATE_SECONDARY_NEGATIVE;
+            }
+        } else if (splitPosition.mStagePosition == STAGE_POSITION_BOTTOM_OR_RIGHT) {
+            // We don't have a bottom option, so should be right
+            return SPLIT_TRANSLATE_PRIMARY_POSITIVE;
+        }
+        throw new IllegalStateException("Invalid split stage position: " +
+                splitPosition.mStagePosition);
+    }
+
     @Override
     public int getPrimaryScroll(View view) {
         return view.getScrollX();