Make COLOR_CONTROL_BACKGROUND customizable from a theme extension

chrome/browser/themes/theme_properties.h

Index: chrome/browser/themes/theme_properties.h
diff --git a/chrome/browser/themes/theme_properties.h b/chrome/browser/themes/theme_properties.h
index 6b323472616c8e674f6bd2c0407de3faf5ccd830..ab8200a5ddc37123109628c0feb94fec2449b8da 100644
--- a/chrome/browser/themes/theme_properties.h
+++ b/chrome/browser/themes/theme_properties.h
@@ -25,6 +25,7 @@ class ThemeProperties {
   // browser_theme_pack.cc.
 
   enum OverwritableByUserThemeProperty {
+    COLOR_CONTROL_BACKGROUND,
     COLOR_FRAME,
     COLOR_FRAME_INACTIVE,
     // Instead of using the INCOGNITO variants directly, most code should
@@ -82,11 +83,9 @@ class ThemeProperties {
   // The enum takes on values >= 1000 as not to overlap with
   // OverwritableByUserThemeProperties.
   enum NotOverwritableByUserThemeProperty {
-    COLOR_CONTROL_BACKGROUND = 1000,
-
     // The color of the line separating the bottom of the toolbar from the
     // contents.
-    COLOR_TOOLBAR_BOTTOM_SEPARATOR,
+    COLOR_TOOLBAR_BOTTOM_SEPARATOR = 1000,
 
     // The color of a normal toolbar button's icon.
     COLOR_TOOLBAR_BUTTON_ICON,