MacViews: draw Mac combobox arrows

ui/views/style/platform_style.h

Index: ui/views/style/platform_style.h
diff --git a/ui/views/style/platform_style.h b/ui/views/style/platform_style.h
index e4240d49306a8920c8f6caf4f26d14b3a7459433..b06fff433a13fb027b46b3412bf3fb5fc4457291 100644
--- a/ui/views/style/platform_style.h
+++ b/ui/views/style/platform_style.h
@@ -20,6 +20,11 @@ class ScrollBar;
 // Cross-platform API for providing platform-specific styling for toolkit-views.
 class PlatformStyle {
  public:
+  // Creates an ImageSkia containing the image to use for the combobox arrow.
+  // The |is_enabled| argument is true if the control the arrow is for is
+  // enabled, and false if the control is disabled.
+  static gfx::ImageSkia CreateComboboxArrow(bool is_enabled);
+
   // Creates the appropriate border for a focusable Combobox.
   static scoped_ptr<FocusableBorder> CreateComboboxBorder();