Add pref to enable/disable palette tray.

ash/shell/shell_delegate_impl.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/shell/shell_delegate_impl.h"
 
 #include "ash/app_list/app_list_presenter_delegate_factory.h"
 #include "ash/common/accessibility_delegate.h"
 #include "ash/common/default_accessibility_delegate.h"
 #include "ash/common/gpu_support_stub.h"
@@ skipping 67 matching lines @@
  private:
   DISALLOW_COPY_AND_ASSIGN(MediaDelegateImpl);
 };
 
 class PaletteDelegateImpl : public PaletteDelegate {
  public:
   PaletteDelegateImpl() {}
   ~PaletteDelegateImpl() override {}
 
   // PaletteDelegate:
+  std::unique_ptr<EnableListenerSubscription> AddPaletteEnableListener(
+      const EnableListener& on_state_changed) override {
+    on_state_changed.Run(false);
+    return nullptr;
+  }
   void CreateNote() override {}
   bool HasNoteApp() override { return false; }
   void SetPartialMagnifierState(bool enabled) override {}
   void SetStylusStateChangedCallback(
       const OnStylusStateChangedCallback& on_stylus_state_changed) override {}
   bool ShouldAutoOpenPalette() override { return false; }
   void TakeScreenshot() override {}
   void TakePartialScreenshot() override {}
 
  private:
@@ skipping 181 matching lines @@
 base::string16 ShellDelegateImpl::GetProductName() const {
   return base::string16();
 }
 
 gfx::Image ShellDelegateImpl::GetDeprecatedAcceleratorImage() const {
   return gfx::Image();
 }
 
 }  // namespace shell
 }  // namespace ash