Add pref to enable/disable palette tray.

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 efea66b7c75610d82abd09e3d6fa8b5b0f166c56..ef47e0a54088077a3e5995bcb07c6b45bf0cc8e9 100644
--- a/ash/shell/shell_delegate_impl.cc
+++ b/ash/shell/shell_delegate_impl.cc
@@ -82,8 +82,15 @@ class MediaDelegateImpl : public MediaDelegate {
 
 class PaletteDelegateImpl : public PaletteDelegate {
  public:
-  PaletteDelegateImpl() {};
-  ~PaletteDelegateImpl() override {};
+  PaletteDelegateImpl() {}
+  ~PaletteDelegateImpl() override {}
+
+  // PaletteDelegate:
+  std::unique_ptr<EnableListenerSubscription> AddPaletteEnableListener(
+      const EnableListener& on_state_changed) override {
+    on_state_changed.Run(false);
+    return std::unique_ptr<EnableListenerSubscription>();

[stevenjb, 2016/08/23 17:36:41]

return nullptr?

[jdufault, 2016/08/23 22:49:56]

Done.

+  }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(PaletteDelegateImpl);