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..1705833c2492ea2a86d8d13a7e411645f36f7732 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 +35,19 @@ 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.
+  // We call InvalidateLayout() so Layout() will get called again next time even
+  // if the bounds haven't changed.
+  if (!layer_owner_) {
+    InvalidateLayout();

[sky, 2016/08/08 19:12:40]

The main thing I don't particularly like about either patch is the explcit call
to invalidatelayout. Can you clarify why it is needed? If you change
InitLayoutOwner() (in either patch) to call Layout() does the need for it go
away?

+    return;
+  }
+
   // Position at 0, 0.
   GetMirrorLayer()->SetBounds(gfx::Rect(GetMirrorLayer()->bounds().size()));
 
@@ -68,6 +61,15 @@ 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 +80,22 @@ 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());
+  }
+}
+
 ui::Layer* WindowMirrorView::GetMirrorLayer() {
   return layer_owner_->root();
 }