linux_aura: Add a flag for experimenting with ARGB windows.

ui/views/widget/desktop_aura/x11_whole_screen_move_loop.cc

Index: ui/views/widget/desktop_aura/x11_whole_screen_move_loop.cc
diff --git a/ui/views/widget/desktop_aura/x11_whole_screen_move_loop.cc b/ui/views/widget/desktop_aura/x11_whole_screen_move_loop.cc
index fa9b75f4efeb59889512169274bc7b9fbe6fb76d..1db4a2226ef5bbe561958d839092029211a053d2 100644
--- a/ui/views/widget/desktop_aura/x11_whole_screen_move_loop.cc
+++ b/ui/views/widget/desktop_aura/x11_whole_screen_move_loop.cc
@@ -363,17 +363,9 @@ void X11WholeScreenMoveLoop::CreateDragImageWindow() {
 }
 
 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) {