Add WindowPinType property on arua::Window

ui/aura/client/aura_constants.h

Index: ui/aura/client/aura_constants.h
diff --git a/ui/aura/client/aura_constants.h b/ui/aura/client/aura_constants.h
index 145188866833e43d3df3cd35722d5fb0a2e23642..203ec669e4252cde73390d25c9b6703bc9b9ac7f 100644
--- a/ui/aura/client/aura_constants.h
+++ b/ui/aura/client/aura_constants.h
@@ -22,6 +22,12 @@ enum class WindowType;
 namespace aura {
 namespace client {
 
+enum class WindowPinType {
+  NONE,
+  PINNED,
+  TRUSTED_PINNED,
+};
+
 enum class WindowEmbedType {
   NONE,
   EMBED_IN_OWNER,
@@ -124,6 +130,13 @@ AURA_EXPORT extern const WindowProperty<SkColor>* const kTopViewColor;
 // A property key to store the window icon, typically 16x16 for title bars.
 AURA_EXPORT extern const WindowProperty<gfx::ImageSkia*>* const kWindowIconKey;
 
+// A property key to store aura::client::WindowPinType for a window.
+// When setting this property to PINNED or TRUSTED_PINNED, the window manager
+// will try to fullscreen the window and pin it on the top of the screen. If the
+// window manager failed to do it, the property will be restored to NONE. When
+// setting this property to NONE, the window manager will restore the window.
+AURA_EXPORT extern const WindowProperty<WindowPinType>* const kWindowPinTypeKey;
+
 // Indicates the type of embedding within the given window.
 AURA_EXPORT extern const WindowProperty<WindowEmbedType>* const kEmbedType;