Implement "pinned" mode in ash.

ash/shelf/shelf_layout_manager.h

Index: ash/shelf/shelf_layout_manager.h
diff --git a/ash/shelf/shelf_layout_manager.h b/ash/shelf/shelf_layout_manager.h
index 15d4559f23b37d8b4004cb162d410bc65ece016c..caf3b7993ed0a88b0228e539e50592a9c13eb622 100644
--- a/ash/shelf/shelf_layout_manager.h
+++ b/ash/shelf/shelf_layout_manager.h
@@ -155,6 +155,7 @@ class ASH_EXPORT ShelfLayoutManager
   void OnLockStateChanged(bool locked) override;
   void OnShelfAlignmentChanged(WmWindow* root_window) override;
   void OnShelfAutoHideBehaviorChanged(WmWindow* root_window) override;
+  void OnPinnedStateChanged(WmWindow* pinned_window) override;
 
   // Overriden from aura::client::ActivationChangeObserver:
   void OnWindowActivated(
@@ -230,7 +231,8 @@ class ASH_EXPORT ShelfLayoutManager
           auto_hide_state(SHELF_AUTO_HIDE_HIDDEN),
           window_state(wm::WORKSPACE_WINDOW_STATE_DEFAULT),
           is_screen_locked(false),
-          is_adding_user_screen(false) {}
+          is_adding_user_screen(false),
+          is_pinned(false) {}
 
     // Returns true if the two states are considered equal. As
     // |auto_hide_state| only matters if |visibility_state| is
@@ -242,7 +244,8 @@ class ASH_EXPORT ShelfLayoutManager
               other.auto_hide_state == auto_hide_state) &&
              other.window_state == window_state &&
              other.is_screen_locked == is_screen_locked &&
-             other.is_adding_user_screen == is_adding_user_screen;
+             other.is_adding_user_screen == is_adding_user_screen &&
+             other.is_pinned == is_pinned;
     }
 
     ShelfVisibilityState visibility_state;
@@ -250,6 +253,7 @@ class ASH_EXPORT ShelfLayoutManager
     wm::WorkspaceWindowState window_state;
     bool is_screen_locked;
     bool is_adding_user_screen;
+    bool is_pinned;
   };
 
   // Sets the visibility of the shelf to |state|.