Add generic PaletteDelegate code.

ash/sysui/shell_delegate_mus.cc

Index: ash/sysui/shell_delegate_mus.cc
diff --git a/ash/sysui/shell_delegate_mus.cc b/ash/sysui/shell_delegate_mus.cc
index 2f36b2fbf56e665d1f2482cc94f52b92437d5909..68a99c77f41cee27af5fb65aa96b39e3c5df8dcb 100644
--- a/ash/sysui/shell_delegate_mus.cc
+++ b/ash/sysui/shell_delegate_mus.cc
@@ -7,6 +7,7 @@
 #include "ash/common/default_accessibility_delegate.h"
 #include "ash/common/gpu_support_stub.h"
 #include "ash/common/media_delegate.h"
+#include "ash/common/palette_delegate.h"
 #include "ash/common/session/session_state_delegate.h"
 #include "ash/common/system/tray/default_system_tray_delegate.h"
 #include "ash/sysui/app_list_presenter_mus.h"
@@ -195,6 +196,11 @@ MediaDelegate* ShellDelegateMus::CreateMediaDelegate() {
   return new MediaDelegateStub;
 }
 
+std::unique_ptr<PaletteDelegate> ShellDelegateMus::CreatePaletteDelegate() {
+  NOTIMPLEMENTED();
+  return nullptr;
+}
+
 std::unique_ptr<PointerWatcherDelegate>
 ShellDelegateMus::CreatePointerWatcherDelegate() {
   return base::WrapUnique(new PointerWatcherDelegateMus);