Display Window Icon In Picker UI

chrome/browser/media/window_icon_util_x11.cc

 // Copyright 2016 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 "chrome/browser/media/window_icon_util.h"
 
 #include <X11/Xatom.h>
 #include <X11/Xutil.h>
 
+#include "ui/gfx/x/x11_error_tracker.h"
 #include "ui/gfx/x/x11_types.h"
 
 gfx::ImageSkia GetWindowIcon(content::DesktopMediaID id) {
   DCHECK(id.type == content::DesktopMediaID::TYPE_WINDOW);
 
   Display* display = gfx::GetXDisplay();
   Atom property = XInternAtom(display, "_NET_WM_ICON", True);
   Atom actual_type;
   int actual_format;
   unsigned long bytes_after;  // NOLINT: type required by XGetWindowProperty
   unsigned long size;
   long* data;
 
+  // The |error_tracker| essentially provides an empty X error handler for

[sky, 2016/08/26 19:38:36]

Excellent description. Thanks!

[qiangchen, 2016/08/26 19:55:24]

Acknowledged.

+  // the call of XGetWindowProperty. The motivation is to guard against crash
+  // for any reason that XGetWindowProperty fails. For example, at the time that
+  // XGetWindowProperty is called, the window handler (a.k.a |id.id|) may
+  // already be invalid due to the fact that the end user has closed the
+  // corresponding window, etc.
+  std::unique_ptr<gfx::X11ErrorTracker> error_tracker(

[Lei Zhang, 2016/08/30 09:39:34]

Can this just be the following?

{
  gfx::X11ErrorTracker error_tracker;
  int status = XGetWindowProperty(...);
}

[qiangchen, 2016/08/30 17:10:45]

By other reviewer's comment, as we want to release it asap, and thus, we set it
in a unique_ptr. Otherwise, we have to wait till the end of this function.

+      new gfx::X11ErrorTracker());
   int status = XGetWindowProperty(display, id.id, property, 0L, ~0L, False,
                                   AnyPropertyType, &actual_type, &actual_format,
                                   &size, &bytes_after,
                                   reinterpret_cast<unsigned char**>(&data));
+  error_tracker.reset();
+
   if (status != Success) {
     return gfx::ImageSkia();
   }
 
   // The format of |data| is concatenation of sections like
   // [width, height, pixel data of size width * height], and the total bytes
   // number of |data| is |size|. And here we are picking the largest icon.
   int width = 0;
   int height = 0;
   int start = 0;
@@ skipping 18 matching lines @@
   for (long y = 0; y < height; ++y) {
     for (long x = 0; x < width; ++x) {
       pixels_data[result.rowBytesAsPixels() * y + x] =
           static_cast<uint32_t>(data[start + width * y + x]);
     }
   }
 
   XFree(data);
   return gfx::ImageSkia::CreateFrom1xBitmap(result);
 }