X11: Use CopyFromParent colormap when possible (Reland)

ui/base/x/x11_util_internal.h

Index: ui/base/x/x11_util_internal.h
diff --git a/ui/base/x/x11_util_internal.h b/ui/base/x/x11_util_internal.h
index 054490da4be4473494f2d561c8179b53250acc8f..3dc852b16ded5a06a4047a23851190bd6ccc30b0 100644
--- a/ui/base/x/x11_util_internal.h
+++ b/ui/base/x/x11_util_internal.h
@@ -63,6 +63,8 @@ class UI_BASE_X_EXPORT XVisualManager {
  public:
   static XVisualManager* GetInstance();
 
+  // Picks the best argb or opaque visual given |want_argb_visual|.  If the
+  // default visual is returned, |colormap| is set to CopyFromParent.
   void ChooseVisualForWindow(bool want_argb_visual,
                              Visual** visual,
                              int* depth,
@@ -101,6 +103,10 @@ class UI_BASE_X_EXPORT XVisualManager {
 
   XDisplay* display_;
 
+  VisualID default_visual_id_;
+
+  // The system visual is usually the same as the default visual, but
+  // may not be in general.
   VisualID system_visual_id_;
   VisualID transparent_visual_id_;