X11: Use CopyFromParent colormap when possible (Reland)

ui/base/x/x11_util_internal.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_BASE_X_X11_UTIL_INTERNAL_H_
 #define UI_BASE_X_X11_UTIL_INTERNAL_H_
 
 // This file declares utility functions for X11 (Linux only).
 //
 // These functions require the inclusion of the Xlib headers. Since the Xlib
@@ skipping 45 matching lines @@
                                                const XErrorEvent& error_event);
 
 // --------------------------------------------------------------------------
 // Selects a visual with a preference for alpha support on compositing window
 // managers.
 #if !defined(OS_CHROMEOS)
 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,
                              Colormap* colormap,
                              bool* using_argb_visual);
 
   // Called by GpuDataManagerImplPrivate when GPUInfo becomes available.  It is
   // necessary for the GPU process to find out which visuals are best for GL
   // because we don't want to load GL in the browser process.  Returns false iff
   // |default_visual_id| or |transparent_visual_id| are invalid.
@@ skipping 18 matching lines @@
    private:
     Colormap colormap_;
   };
 
   XVisualManager();
 
   std::unordered_map<VisualID, std::unique_ptr<XVisualData>> visuals_;
 
   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_;
 
   bool using_compositing_wm_;
   bool using_software_rendering_;
   bool have_gpu_argb_visual_;
 
   DISALLOW_COPY_AND_ASSIGN(XVisualManager);
 };
 #endif
 
 }  // namespace ui
 
 #endif  // UI_BASE_X_X11_UTIL_INTERNAL_H_