Views: factor out Combobox background and const-ify style

ui/views/controls/combobox/combobox.h

Index: ui/views/controls/combobox/combobox.h
diff --git a/ui/views/controls/combobox/combobox.h b/ui/views/controls/combobox/combobox.h
index 2705f7e22cc57e836ec64d03223a41bce479a585..a3112c7eb9cde23f28b21540bd644672fe5810f3 100644
--- a/ui/views/controls/combobox/combobox.h
+++ b/ui/views/controls/combobox/combobox.h
@@ -53,7 +53,7 @@ class VIEWS_EXPORT Combobox : public PrefixDelegate, public ButtonListener {
   static const char kViewClassName[];
 
   // |model| is not owned by the combobox.
-  explicit Combobox(ui::ComboboxModel* model);
+  explicit Combobox(ui::ComboboxModel* model, Style style = STYLE_NORMAL);
   ~Combobox() override;
 
   static const gfx::FontList& GetFontList();
@@ -61,8 +61,6 @@ class VIEWS_EXPORT Combobox : public PrefixDelegate, public ButtonListener {
   // Sets the listener which will be called when a selection has been made.
   void set_listener(ComboboxListener* listener) { listener_ = listener; }
 
-  void SetStyle(Style style);
-
   // Informs the combobox that its model changed.
   void ModelChanged();
 
@@ -85,10 +83,6 @@ class VIEWS_EXPORT Combobox : public PrefixDelegate, public ButtonListener {
   void SetInvalid(bool invalid);
   bool invalid() const { return invalid_; }
 
-  // Returns the width of the arrow button component of the combobox: the arrow
-  // button itself, and the padding on either side of it.
-  int GetArrowButtonWidth() const;
-
   // Overridden from View:
   gfx::Size GetPreferredSize() const override;
   const char* GetClassName() const override;
@@ -100,6 +94,7 @@ class VIEWS_EXPORT Combobox : public PrefixDelegate, public ButtonListener {
   void OnBlur() override;
   void GetAccessibleState(ui::AXViewState* state) override;
   void Layout() override;
+  void OnEnabledChanged() override;
 
   // Overridden from PrefixDelegate:
   int GetRowCount() override;
@@ -148,11 +143,14 @@ class VIEWS_EXPORT Combobox : public PrefixDelegate, public ButtonListener {
 
   PrefixSelector* GetPrefixSelector();
 
+  // Returns the width of the combobox's arrow container.
+  int GetArrowContainerWidth() const;
+
   // Our model. Not owned.
   ui::ComboboxModel* model_;
 
   // The visual style of this combobox.
-  Style style_;
+  const Style style_;
 
   // Our listener. Not owned. Notified when the selected index change.
   ComboboxListener* listener_;
@@ -203,6 +201,9 @@ class VIEWS_EXPORT Combobox : public PrefixDelegate, public ButtonListener {
   // destroyed.
   std::unique_ptr<views::MenuRunner> menu_runner_;
 
+  // The image to be drawn for this combobox's arrow.
+  gfx::ImageSkia arrow_image_;
+
   // Used for making calbacks.
   base::WeakPtrFactory<Combobox> weak_ptr_factory_;