mash: Add WmShell::SetDisplayWorkAreaInsets for ShelfLayoutManager.

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 7215b943997d0c5997615e5b5cc2888a99eff7e6..254b52b14ab110750b329684b314f92821d00fc4 100644
--- a/ash/mus/bridge/wm_shell_mus.cc
+++ b/ash/mus/bridge/wm_shell_mus.cc
@@ -240,6 +240,11 @@ bool WmShellMus::IsForceMaximizeOnFirstRun() {
   return false;
 }
 
+void WmShellMus::SetDisplayWorkAreaInsets(WmWindow* window,
+                                          const gfx::Insets& insets) {
+  NOTIMPLEMENTED();
+}
+
 bool WmShellMus::IsPinned() {
   NOTIMPLEMENTED();
   return false;