Remove unused references to NativeTheme in TrayPopupItemStyle.

ash/common/system/chromeos/palette/palette_tray.cc

Index: ash/common/system/chromeos/palette/palette_tray.cc
diff --git a/ash/common/system/chromeos/palette/palette_tray.cc b/ash/common/system/chromeos/palette/palette_tray.cc
index affb069a96ac98dc68c1b26ba55b27bc308c4e60..d2bccbee2c9bd066672aa7f912a7fde89a7a3740 100644
--- a/ash/common/system/chromeos/palette/palette_tray.cc
+++ b/ash/common/system/chromeos/palette/palette_tray.cc
@@ -84,11 +84,13 @@ class TitleView : public views::View, public views::ButtonListener {
         new views::BoxLayout(views::BoxLayout::kHorizontal, 0, 0, 0);
     SetLayoutManager(box_layout);
 
-    title_label_ =
+    auto title_label =
         new views::Label(l10n_util::GetStringUTF16(IDS_ASH_STYLUS_TOOLS_TITLE));
-    title_label_->SetHorizontalAlignment(gfx::ALIGN_LEFT);
-    AddChildView(title_label_);
-    box_layout->SetFlexForView(title_label_, 1);
+    title_label->SetHorizontalAlignment(gfx::ALIGN_LEFT);
+    AddChildView(title_label);
+    TrayPopupItemStyle style(TrayPopupItemStyle::FontStyle::TITLE);
+    style.SetupLabel(title_label);
+    box_layout->SetFlexForView(title_label, 1);
     if (MaterialDesignController::IsSystemTrayMenuMaterial()) {
       help_button_ =
           new SystemMenuButton(this, TrayPopupInkDropStyle::HOST_CENTERED,
@@ -122,11 +124,6 @@ class TitleView : public views::View, public views::ButtonListener {
   ~TitleView() override {}
 
  private:
-  // views::View:
-  void OnNativeThemeChanged(const ui::NativeTheme* theme) override {
-    UpdateStyle();
-  }
-
   // views::ButtonListener:
   void ButtonPressed(views::Button* sender, const ui::Event& event) override {
     if (sender == settings_button_) {
@@ -144,18 +141,10 @@ class TitleView : public views::View, public views::ButtonListener {
     }
   }
 
-  void UpdateStyle() {
-    TrayPopupItemStyle style(GetNativeTheme(),
-                             TrayPopupItemStyle::FontStyle::TITLE);
-    style.SetupLabel(title_label_);
-  }
-
   // Unowned pointers to button views so we can determine which button was
   // clicked.
   views::View* settings_button_;
   views::View* help_button_;
-  // Needed for UpdateStyles()
-  views::Label* title_label_;
   PaletteTray* palette_tray_;
 
   DISALLOW_COPY_AND_ASSIGN(TitleView);