Add generic PaletteDelegate code.

ash/shell/shell_delegate_impl.cc

Index: ash/shell/shell_delegate_impl.cc
diff --git a/ash/shell/shell_delegate_impl.cc b/ash/shell/shell_delegate_impl.cc
index e8151465026b4f2b908796001e5ce0daff9c008f..efea66b7c75610d82abd09e3d6fa8b5b0f166c56 100644
--- a/ash/shell/shell_delegate_impl.cc
+++ b/ash/shell/shell_delegate_impl.cc
@@ -10,6 +10,7 @@
 #include "ash/common/gpu_support_stub.h"
 #include "ash/common/media_delegate.h"
 #include "ash/common/new_window_delegate.h"
+#include "ash/common/palette_delegate.h"
 #include "ash/common/session/session_state_delegate.h"
 #include "ash/common/shell_window_ids.h"
 #include "ash/common/system/tray/default_system_tray_delegate.h"
@@ -79,6 +80,15 @@ class MediaDelegateImpl : public MediaDelegate {
   DISALLOW_COPY_AND_ASSIGN(MediaDelegateImpl);
 };
 
+class PaletteDelegateImpl : public PaletteDelegate {
+ public:
+  PaletteDelegateImpl() {};
+  ~PaletteDelegateImpl() override {};
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(PaletteDelegateImpl);
+};
+
 class SessionStateDelegateImpl : public SessionStateDelegate {
  public:
   SessionStateDelegateImpl()
@@ -243,6 +253,10 @@ ash::MediaDelegate* ShellDelegateImpl::CreateMediaDelegate() {
   return new MediaDelegateImpl;
 }
 
+std::unique_ptr<PaletteDelegate> ShellDelegateImpl::CreatePaletteDelegate() {
+  return base::WrapUnique(new PaletteDelegateImpl());
+}
+
 std::unique_ptr<ash::PointerWatcherDelegate>
 ShellDelegateImpl::CreatePointerWatcherDelegate() {
   return base::WrapUnique(new PointerWatcherDelegateAura);