Keep split bounds after configuration update

Before this change, split bounds always reset to half-half if
rotation. This is weird on large screen devices because they can
scale bounds in landscape too, so bounds will reset even if from
landscape to seascape.

Add restore mechanism by compute ration of current divider
and total length. Use this ratio to compute estimate position in
new configuration then get suitable snap target. Update divider
position and split bounds by this snap target postition.

Fix: 192533269
Test: pass existing tests
Test: Set density to large screen, active stage split and make top
      task larger then rotate to landscape.
Change-Id: I3ea12273348575ae968c76bdf9236155380526ec

libs/WindowManager/Shell/src/com/android/wm/shell/common/split/SplitLayout.java

@@ -92,6 +92,7 @@ public final class SplitLayout {
     private final Rect mDividerBounds = new Rect();
     private final Rect mBounds1 = new Rect();
     private final Rect mBounds2 = new Rect();
+    private final Rect mTmpBounds = new Rect();
     private final SplitLayoutHandler mSplitLayoutHandler;
     private final SplitWindowManager mSplitWindowManager;
     private final DisplayImeController mDisplayImeController;
@@ -187,9 +188,10 @@ public final class SplitLayout {
         final int rotation = configuration.windowConfiguration.getRotation();
         final Rect rootBounds = configuration.windowConfiguration.getBounds();
         if (rotation != mRotation || !mRootBounds.equals(rootBounds)) {
+            mTmpBounds.set(mRootBounds);
             mRootBounds.set(rootBounds);
             mDividerSnapAlgorithm = getSnapAlgorithm(mContext, mRootBounds);
-            resetDividerPosition();
+            initDividerPosition(mTmpBounds);
             affectsLayout = true;
         }
 
@@ -201,6 +203,19 @@ public final class SplitLayout {
         return affectsLayout;
     }
 
+    private void initDividerPosition(Rect oldBounds) {
+        final float snapRatio = (float) mDividePosition
+                / (float) (isLandscape(oldBounds) ? oldBounds.width() : oldBounds.height());
+        // Estimate position by previous ratio.
+        final float length =
+                (float) (isLandscape() ? mRootBounds.width() : mRootBounds.height());
+        final int estimatePosition = (int) (length * snapRatio);
+        // Init divider position by estimated position using current bounds snap algorithm.
+        mDividePosition = mDividerSnapAlgorithm.calculateNonDismissingSnapTarget(
+                estimatePosition).position;
+        updateBounds(mDividePosition);
+    }
+
     /** Updates recording bounds of divider window and both of the splits. */
     private void updateBounds(int position) {
         mDividerBounds.set(mRootBounds);