Implement "pinned" mode in ash.

ash/mus/bridge/wm_shell_mus.cc

Index: ash/mus/bridge/wm_shell_mus.cc
diff --git a/ash/mus/bridge/wm_shell_mus.cc b/ash/mus/bridge/wm_shell_mus.cc
index ae04940bc5490e15089d4418c22301d98c9672ad..d21336b84eac59255eda2890f2c96d4d1372c555 100644
--- a/ash/mus/bridge/wm_shell_mus.cc
+++ b/ash/mus/bridge/wm_shell_mus.cc
@@ -182,6 +182,15 @@ bool WmShellMus::IsForceMaximizeOnFirstRun() {
   return false;
 }
 
+bool WmShellMus::IsPinned() {
+  NOTIMPLEMENTED();
+  return false;
+}
+
+void WmShellMus::SetPinnedWindow(WmWindow* window) {
+  NOTIMPLEMENTED();
+}
+
 bool WmShellMus::CanShowWindowForUser(WmWindow* window) {
   NOTIMPLEMENTED();
   return true;
@@ -265,10 +274,6 @@ void WmShellMus::RemoveShellObserver(ShellObserver* observer) {
   wm_shell_common_->RemoveShellObserver(observer);
 }
 
-void WmShellMus::NotifyPinnedStateChanged(WmWindow* pinned_window) {
-  wm_shell_common_->NotifyPinnedStateChanged(pinned_window);
-}
-
 // static
 bool WmShellMus::IsActivationParent(::mus::Window* window) {
   return window && IsActivatableShellWindowId(