Repaint window when moving across displays

The paint cache used by layer paint delegates(views) do not work well
with Mirrored layers that are on different device scale factor.

This patch forces a schedule repaint when the user stops dragging the
window so that the invalid data in PaintCache is not used.

Bug: 786628
Change-Id: Ic249d592d4f93b47dc4ede4461f44a59ce7b18d7
Component: Window, Drag window, phantom window
Reviewed-on: https://chromium-review.googlesource.com/1028620Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Commit-Queue: Malay Keshav <malaykeshav@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553812}

ash/wm/drag_window_resizer.cc

@@ -23,6 +23,17 @@
 #include "ui/wm/core/window_util.h"
 
 namespace ash {
+namespace {
+
+void RecursiveSchedulePainter(ui::Layer* layer) {
+  if (!layer)
+    return;
+  layer->SchedulePaint(gfx::Rect(layer->size()));
+  for (auto* child : layer->children())
+    RecursiveSchedulePainter(child);
+}
+
+}  // namespace
 
 // static
 DragWindowResizer* DragWindowResizer::instance_ = NULL;
@@ -67,6 +78,10 @@ void DragWindowResizer::CompleteDrag() {
   GetTarget()->layer()->SetOpacity(details().initial_opacity);
   drag_window_controller_.reset();
 
+  // TODO(malaykeshav) - This is temporary fix/workaround that keeps performance
+  // but may not give the best UI while dragging. See https://crbug/834114
+  RecursiveSchedulePainter(GetTarget()->layer());
+
   // Check if the destination is another display.
   gfx::Point last_mouse_location_in_screen = last_mouse_location_;
   ::wm::ConvertPointToScreen(GetTarget()->parent(),