Implement "pinned" mode in ash.

ash/aura/wm_shell_aura.cc

Index: ash/aura/wm_shell_aura.cc
diff --git a/ash/aura/wm_shell_aura.cc b/ash/aura/wm_shell_aura.cc
index b0444b74ec98cafa892b116b1ff9c71fcd20a0e5..d556a26506cae43506c755bfdde55581bd39990f 100644
--- a/ash/aura/wm_shell_aura.cc
+++ b/ash/aura/wm_shell_aura.cc
@@ -16,6 +16,7 @@
 #include "ash/shell_delegate.h"
 #include "ash/wm/drag_window_resizer.h"
 #include "ash/wm/overview/window_selector_controller.h"
+#include "ash/wm/screen_pinning_controller.h"
 #include "ash/wm/window_util.h"
 #include "base/memory/ptr_util.h"
 #include "ui/aura/client/focus_client.h"
@@ -79,6 +80,10 @@ bool WmShellAura::IsForceMaximizeOnFirstRun() {
   return Shell::GetInstance()->delegate()->IsForceMaximizeOnFirstRun();
 }
 
+bool WmShellAura::IsPinned() {
+  return Shell::GetInstance()->screen_pinning_controller()->IsPinned();
+}
+
 bool WmShellAura::CanShowWindowForUser(WmWindow* window) {
   return Shell::GetInstance()->delegate()->CanShowWindowForUser(window);
 }