Converts most of WorkspaceLayoutManager tests to use common code

ash/common/wm_window.h

Index: ash/common/wm_window.h
diff --git a/ash/common/wm_window.h b/ash/common/wm_window.h
index a02cbf743d5aedbe69a52dc5c9e9c1f590620ea4..3871d2f01262bbedf8a3fff432a015187d2719a3 100644
--- a/ash/common/wm_window.h
+++ b/ash/common/wm_window.h
@@ -94,9 +94,12 @@ class ASH_EXPORT WmWindow {
 
   virtual bool IsBubble() = 0;
 
-  // TODO(sky): seems like this shouldn't be exposed.
   virtual ui::Layer* GetLayer() = 0;
 
+  // TODO(sky): these are temporary until GetLayer() always returns non-null.
+  virtual bool GetLayerTargetVisibility() = 0;
+  virtual bool GetLayerVisible() = 0;
+
   virtual display::Display GetDisplayNearestWindow() = 0;
 
   virtual bool HasNonClientArea() = 0;
@@ -238,6 +241,9 @@ class ASH_EXPORT WmWindow {
 
   virtual bool HasRestoreBounds() const = 0;
 
+  // See ScreenPinningController::SetPinnedWindow() for details.

[msw, 2016/10/06 20:18:24]

aside: The comment there is: "Sets a pinned window. It is not allowed to call
this when there already is a pinned window." Something should actually explain
what it means for a window to be pinned. Maybe reference wm::PinWindow(), which
gives a better explanation: "Pins the window on top of other windows." (ie.
always-on-top [local to some container?])

[sky, 2016/10/06 21:05:58]

I completely agree with on the lack of documentation for pinning, but I tend to
think that is out of scope of this patch (ScreenPinningController should be the
one describing all this). Even pins on top of other windows doesn't really
describe it in detail.

[msw, 2016/10/06 21:19:16]

Acknowledged.

+  virtual void SetPinned(bool trusted) = 0;
+
   virtual void SetAlwaysOnTop(bool value) = 0;
   virtual bool IsAlwaysOnTop() const = 0;