Display Window Icon In Picker UI

chrome/browser/media/window_icon_util_x11.cc

Index: chrome/browser/media/window_icon_util_x11.cc
diff --git a/chrome/browser/media/window_icon_util_x11.cc b/chrome/browser/media/window_icon_util_x11.cc
index 36462dc229d131d6adbc58c1fadb4b26427e3624..6af2fa23e3d75bc653234ca90d07ac87c92b0f5a 100644
--- a/chrome/browser/media/window_icon_util_x11.cc
+++ b/chrome/browser/media/window_icon_util_x11.cc
@@ -9,6 +9,10 @@
 
 #include "ui/gfx/x/x11_types.h"
 
+int ErrorHandler(Display* display, XErrorEvent* event) {

[msw, 2016/08/24 17:01:28]

Why is this needed? Can you add an explanatory comment?

[qiangchen, 2016/08/24 18:03:30]

Done.

+  return 0;
+}
+
 gfx::ImageSkia GetWindowIcon(content::DesktopMediaID id) {
   DCHECK(id.type == content::DesktopMediaID::TYPE_WINDOW);
 
@@ -20,6 +24,7 @@ gfx::ImageSkia GetWindowIcon(content::DesktopMediaID id) {
   unsigned long size;
   long* data;
 
+  XSetErrorHandler(&ErrorHandler);
   int status = XGetWindowProperty(display, id.id, property, 0L, ~0L, False,
                                   AnyPropertyType, &actual_type, &actual_format,
                                   &size, &bytes_after,
@@ -27,6 +32,7 @@ gfx::ImageSkia GetWindowIcon(content::DesktopMediaID id) {
   if (status != Success) {
     return gfx::ImageSkia();
   }
+  XSetErrorHandler(nullptr);

[msw, 2016/08/24 17:01:28]

Cache the old handler and restore it afterwards, like other callers:
auto old_error_handler = XSetErrorHandler(&ErrorHandler);
...
XSetErrorHandler(old_error_handler);

[qiangchen, 2016/08/24 18:03:30]

Is this quite useful here? The error handler is just a function pointer.
&ErrorHandler is a const. Doing caching is just like store a const in a
variable, and reuse it later.

[msw, 2016/08/24 18:13:56]

My thought is that there may be some pre-existing error handler before you call
XSetErrorHandler, but when you're all done here, you set it to null, instead of
restoring the pre-existing error handler.

[qiangchen, 2016/08/24 18:59:13]

Done.

 
   // The format of |data| is concatenation of sections like
   // [width, height, pixel data of size width * height], and the total bytes