Add temporary debug logging for crbug.com/639350.

ui/base/test/ui_controls.h

Index: ui/base/test/ui_controls.h
diff --git a/ui/base/test/ui_controls.h b/ui/base/test/ui_controls.h
index 4fc54abb126c56a822c587540300e742c586f143..f11daae81775a049a8cf3a16f0b67d330a33d3dc 100644
--- a/ui/base/test/ui_controls.h
+++ b/ui/base/test/ui_controls.h
@@ -12,6 +12,9 @@
 
 namespace ui_controls {
 
+// TODO(msw): Remove flaky test debug logging for http://crbug.com/639350.
+extern bool g_crbug_639350_logging;
+
 // A set of utility functions to generate native events in platform
 // independent way. Note that since the implementations depend on a window being
 // top level, these can only be called from test suites that are not sharded.