Wrap route transitions above the transition as well to prevent repaints (#15534)

packages/flutter/lib/src/widgets/routes.dart

@@ -466,19 +466,23 @@ class _ModalScopeState extends State<_ModalScope> {
         offstage: widget.route.offstage,
         child: new IgnorePointer(
           ignoring: widget.route.animation?.status == AnimationStatus.reverse,
-          child: widget.route.buildTransitions(
-            context,
-            widget.route.animation,
-            widget.route.secondaryAnimation,
-            new RepaintBoundary(
-              child: new PageStorage(
-                key: widget.route._subtreeKey,
-                bucket: widget.route._storageBucket,
-                child: new _ModalScopeStatus(
-                  route: widget.route,
-                  isCurrent: widget.route.isCurrent,
-                  canPop: widget.route.canPop,
-                  child: widget.page,
+          // Keep the transition between repaint boundaries so we don't trigger
+          // deep repaints of the render tree above or below the transition.
+          child: new RepaintBoundary(
+            child: widget.route.buildTransitions(
+              context,
+              widget.route.animation,
+              widget.route.secondaryAnimation,
+              new RepaintBoundary(
+                child: new PageStorage(
+                  key: widget.route._subtreeKey,
+                  bucket: widget.route._storageBucket,
+                  child: new _ModalScopeStatus(
+                    route: widget.route,
+                    isCurrent: widget.route.isCurrent,
+                    canPop: widget.route.canPop,
+                    child: widget.page,
+                  ),
                 ),
               ),
             ),