linux_aura: Add a flag for experimenting with ARGB windows.

ui/views/widget/desktop_aura/x11_whole_screen_move_loop.cc

 // Copyright (c) 2012 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.
 
 #include "ui/views/widget/desktop_aura/x11_whole_screen_move_loop.h"
 
 #include <X11/Xlib.h>
 // Get rid of a macro from Xlib.h that conflicts with Aura's RootWindow class.
 #undef RootWindow
 
@@ skipping 345 matching lines @@
   image->SetImage(drag_image_);
   image->SetBounds(0, 0, drag_image_.width(), drag_image_.height());
   widget->SetContentsView(image);
   widget->Show();
   widget->GetNativeWindow()->layer()->SetFillsBoundsOpaquely(false);
 
   drag_widget_.reset(widget);
 }
 
 bool X11WholeScreenMoveLoop::CheckIfIconValid() {
-  // TODO(erg): I've tried at least five different strategies for trying to
-  // build a mask based off the alpha channel. While all of them have worked,
-  // none of them have been performant and introduced multiple second
-  // delays. (I spent a day getting a rectangle segmentation algorithm polished
-  // here...and then found that even through I had the rectangle extraction
-  // down to mere milliseconds, SkRegion still fell over on the number of
-  // rectangles.)
-  //
-  // Creating a mask here near instantaneously should be possible, as GTK does
-  // it, but I've blown days on this and I'm punting now.
-
+  // Because we need a GL context per window, we do a quick check so that we
+  // don't make another context if the window would just be displaying a mostly
+  // transparent image.
   const SkBitmap* in_bitmap = drag_image_.bitmap();
   SkAutoLockPixels in_lock(*in_bitmap);
   for (int y = 0; y < in_bitmap->height(); ++y) {
     uint32* in_row = in_bitmap->getAddr32(0, y);
 
     for (int x = 0; x < in_bitmap->width(); ++x) {
       if (SkColorGetA(in_row[x]) > kMinAlpha)
         return true;
     }
   }
 
   return false;
 }
 
 }  // namespace views