Update initial staged split UX.

- Introduce inset to the staged split view
- Update width of the staged split view
- Introduce rounded corners to staged split view. It's tricky to animate it in with smooth transition considering the rounded corners. The best way to handle it is to draw content as if part of it is off the screen, so that when it's animated in, the rounded corners can slide in onto the screen correctly.

Fixes: 219085340
Test: https://recall.googleplex.com/projects/f46cfe9c-8076-4efe-bf8a-b1cc4f1f5e1b/sessions/09a99b75-3614-4d20-b6d4-a78108f769d8

Change-Id: I24d90cc9e2695d822cb2de8b21e2d5519f2e344d

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

@@ -393,12 +393,21 @@ public class LandscapePagedViewHandler implements PagedOrientationHandler {
     }
 
     @Override
-    public void getInitialSplitPlaceholderBounds(int placeholderHeight, DeviceProfile dp,
-            @StagePosition int stagePosition, Rect out) {
+    public void getInitialSplitPlaceholderBounds(int placeholderHeight, int placeholderInset,
+            DeviceProfile dp, @StagePosition int stagePosition, Rect out) {
         // In fake land/seascape, the placeholder always needs to go to the "top" of the device,
         // which is the same bounds as 0 rotation.
         int width = dp.widthPx;
         out.set(0, 0, width, placeholderHeight);
+        out.inset(placeholderInset, 0);
+
+        // Adjust the top to account for content off screen. This will help to animate the view in
+        // with rounded corners.
+        int screenWidth = dp.widthPx;
+        int screenHeight = dp.heightPx;
+        int totalHeight = (int) (1.0f * screenHeight / 2 * (screenWidth - 2 * placeholderInset)
+                / screenWidth);
+        out.top -= (totalHeight - placeholderHeight);
     }
 
     @Override