Ash window cycle ui: don't create mirrored layers for previews until

ash/wm/window_mirror_view.cc

Index: ash/wm/window_mirror_view.cc
diff --git a/ash/wm/window_mirror_view.cc b/ash/wm/window_mirror_view.cc
index 1c50ecb5a2e7ed5a4c87b8bfb2eaf67644541ac6..e797dc9f1d7cccbafe8ebdf75ae293ddfd9fe81d 100644
--- a/ash/wm/window_mirror_view.cc
+++ b/ash/wm/window_mirror_view.cc
@@ -11,6 +11,7 @@
 #include "ui/aura/window.h"
 #include "ui/compositor/layer.h"
 #include "ui/compositor/layer_tree_owner.h"
+#include "ui/views/widget/widget.h"
 
 namespace ash {
 namespace wm {
@@ -34,27 +35,15 @@ WindowMirrorView::WindowMirrorView(WmWindowAura* window) : target_(window) {
 }
 WindowMirrorView::~WindowMirrorView() {}
 
-void WindowMirrorView::Init() {
-  SetPaintToLayer(true);
-
-  layer_owner_ = ::wm::RecreateLayers(target_->aura_window(), this);
-
-  GetMirrorLayer()->parent()->Remove(GetMirrorLayer());
-  layer()->Add(GetMirrorLayer());
-
-  // Some extra work is needed when the target window is minimized.
-  if (target_->GetWindowState()->IsMinimized()) {
-    GetMirrorLayer()->SetVisible(true);
-    GetMirrorLayer()->SetOpacity(1);
-    EnsureAllChildrenAreVisible(GetMirrorLayer());
-  }
-}
-
 gfx::Size WindowMirrorView::GetPreferredSize() const {
   return target_->GetBounds().size();
 }
 
 void WindowMirrorView::Layout() {
+  // If |layer_owner_| hasn't been initialized (|this| isn't on screen), no-op.
+  if (!layer_owner_)
+    return;
+
   // Position at 0, 0.
   GetMirrorLayer()->SetBounds(gfx::Rect(GetMirrorLayer()->bounds().size()));
 
@@ -68,6 +57,15 @@ void WindowMirrorView::Layout() {
   GetMirrorLayer()->SetTransform(mirror_transform);
 }
 
+bool WindowMirrorView::GetNeedsNotificationWhenVisibleBoundsChange() const {
+  return true;
+}
+
+void WindowMirrorView::OnVisibleBoundsChanged() {
+  if (!layer_owner_ && !GetVisibleBounds().IsEmpty())
+    InitLayerOwner();
+}
+
 ui::LayerDelegate* WindowMirrorView::CreateDelegate(
     ui::LayerDelegate* delegate) {
   if (!delegate)
@@ -78,6 +76,24 @@ ui::LayerDelegate* WindowMirrorView::CreateDelegate(
   return delegates_.back().get();
 }
 
+void WindowMirrorView::InitLayerOwner() {
+  SetPaintToLayer(true);
+
+  layer_owner_ = ::wm::RecreateLayers(target_->aura_window(), this);
+
+  GetMirrorLayer()->parent()->Remove(GetMirrorLayer());
+  layer()->Add(GetMirrorLayer());
+
+  // Some extra work is needed when the target window is minimized.
+  if (target_->GetWindowState()->IsMinimized()) {
+    GetMirrorLayer()->SetVisible(true);
+    GetMirrorLayer()->SetOpacity(1);
+    EnsureAllChildrenAreVisible(GetMirrorLayer());
+  }
+
+  Layout();
+}
+
 ui::Layer* WindowMirrorView::GetMirrorLayer() {
   return layer_owner_->root();
 }