Allow a View to specify a non-default native theme (i.e. different from

ui/views/view.h

Index: ui/views/view.h
diff --git a/ui/views/view.h b/ui/views/view.h
index 21daecf973235757f1252ccbf21d88aca4756cf3..147785c6a86b255dc5e279a35c33d7bb0b7aa76b 100644
--- a/ui/views/view.h
+++ b/ui/views/view.h
@@ -539,14 +539,18 @@ class VIEWS_EXPORT View : public ui::LayerDelegate,
 
   // Returns the NativeTheme to use for this View. This calls through to
   // GetNativeTheme() on the Widget this View is in, or provides a default
-  // theme if there's no widget. Warning: the default theme might not be
-  // correct; you should probably override OnNativeThemeChanged().
+  // theme if there's no widget, or returns |native_theme_| if that's
+  // set. Warning: the default theme might not be correct; you should probably
+  // override OnNativeThemeChanged().
   ui::NativeTheme* GetNativeTheme() {
     return const_cast<ui::NativeTheme*>(
         const_cast<const View*>(this)->GetNativeTheme());
   }
   const ui::NativeTheme* GetNativeTheme() const;
 
+  // Sets the native theme and informs descendants.
+  void SetNativeTheme(ui::NativeTheme* theme);
+
   // RTL painting --------------------------------------------------------------
 
   // This method determines whether the gfx::Canvas object passed to
@@ -1547,6 +1551,13 @@ class VIEWS_EXPORT View : public ui::LayerDelegate,
   // Cached output of painting to be reused in future frames until invalidated.
   ui::PaintCache paint_cache_;
 
+  // Native theme --------------------------------------------------------------
+
+  // A native theme for this view and its descendants. Typically null, in which
+  // case the native theme is drawn from the parent view (eventually the
+  // widget).
+  ui::NativeTheme* native_theme_ = nullptr;
+
   // RTL painting --------------------------------------------------------------
 
   // Indicates whether or not the gfx::Canvas object passed to View::Paint()