Add support for drawing window caption buttons on windows.

ui/native_theme/native_theme.h

Index: ui/native_theme/native_theme.h
diff --git a/ui/native_theme/native_theme.h b/ui/native_theme/native_theme.h
index a9f56d5d6d9d1a0d4094603879e366d31d3b4ead..6f071f0de4f16d593e753fe266651fb71d2f1ec2 100644
--- a/ui/native_theme/native_theme.h
+++ b/ui/native_theme/native_theme.h
@@ -84,6 +84,13 @@ class NATIVE_THEME_EXPORT NativeTheme {
     kTrackbarThumb,
     kTrackbarTrack,
     kWindowResizeGripper,
+
+    // Parts used in the title bar of the window.
+    kCaptionMin,
+    kCaptionMax,
+    kCaptionRestore,
+    kCaptionClose,
+
     kMaxPart,
   };