aura: Remove layerless windows.

Layerless windows are only used in unit tests today, and add
complexity in that a NativeWidgetAura can not rely on there
being a layer present. In practice, having a layer per Window
is not unreasonable overhead, and is simpler. The way to render
something into the same layer is to use a separate View instead
of a separate Window.

R=sky
BUG=466426

Review URL: https://codereview.chromium.org/1050713002

Cr-Commit-Position: refs/heads/master@{#323610}
diff --git a/ui/aura/demo/demo_main.cc b/ui/aura/demo/demo_main.cc
index e7ed3680..2e4ac3b 100644
--- a/ui/aura/demo/demo_main.cc
+++ b/ui/aura/demo/demo_main.cc
@@ -156,7 +156,7 @@
   DemoWindowDelegate window_delegate1(SK_ColorBLUE);
   aura::Window window1(&window_delegate1);
   window1.set_id(1);
-  window1.Init(aura::WINDOW_LAYER_TEXTURED);
+  window1.Init(ui::LAYER_TEXTURED);
   window1.SetBounds(gfx::Rect(100, 100, 400, 400));
   window1.Show();
   aura::client::ParentWindowWithContext(&window1, host->window(), gfx::Rect());
@@ -164,7 +164,7 @@
   DemoWindowDelegate window_delegate2(SK_ColorRED);
   aura::Window window2(&window_delegate2);
   window2.set_id(2);
-  window2.Init(aura::WINDOW_LAYER_TEXTURED);
+  window2.Init(ui::LAYER_TEXTURED);
   window2.SetBounds(gfx::Rect(200, 200, 350, 350));
   window2.Show();
   aura::client::ParentWindowWithContext(&window2, host->window(), gfx::Rect());
@@ -172,7 +172,7 @@
   DemoWindowDelegate window_delegate3(SK_ColorGREEN);
   aura::Window window3(&window_delegate3);
   window3.set_id(3);
-  window3.Init(aura::WINDOW_LAYER_TEXTURED);
+  window3.Init(ui::LAYER_TEXTURED);
   window3.SetBounds(gfx::Rect(10, 10, 50, 50));
   window3.Show();
   window2.AddChild(&window3);