Partial fix for jumping freeform windows

Currently every focus change causes a freeform window to jump
for a few frames. The size of the jump is equal to the difference
in inset size (which is derived directly from the window elevation).

This problem goes away for most real use cases if the insets are
not allowed to decrease.

Bug: 28318973
Bug: 22668382
Change-Id: I77ca440a7d9c89cc4d45e6667bf37da94a5c8a9a

core/java/android/view/WindowManager.java

@@ -1803,7 +1803,21 @@ public interface WindowManager extends ViewManager {
          */
         public final void setSurfaceInsets(View view, boolean manual, boolean preservePrevious) {
             final int surfaceInset = (int) Math.ceil(view.getZ() * 2);
-            surfaceInsets.set(surfaceInset, surfaceInset, surfaceInset, surfaceInset);
+            // Partial workaround for b/28318973. Every inset change causes a freeform window
+            // to jump a little for a few frames. If we never allow surface insets to decrease,
+            // they will stabilize quickly (often from the very beginning, as most windows start
+            // as focused).
+            // TODO(b/22668382) to fix this properly.
+            if (surfaceInset == 0) {
+                // OK to have 0 (this is the case for non-freeform windows).
+                surfaceInsets.set(0, 0, 0, 0);
+            } else {
+                surfaceInsets.set(
+                        Math.max(surfaceInset, surfaceInsets.left),
+                        Math.max(surfaceInset, surfaceInsets.top),
+                        Math.max(surfaceInset, surfaceInsets.right),
+                        Math.max(surfaceInset, surfaceInsets.bottom));
+            }
             hasManualSurfaceInsets = manual;
             preservePreviousSurfaceInsets = preservePrevious;
         }