Move gtk_settings_get_default() call to the UI thread.

base/mime_util.h

Index: base/mime_util.h
===================================================================
--- base/mime_util.h	(revision 23879)
+++ base/mime_util.h	(working copy)
@@ -20,6 +20,13 @@
 // Get the mime type for a byte vector.
 std::string GetDataMimeType(const std::string& data);
 
+#if defined(OS_LINUX)
+// This detects the current GTK theme by calling gtk_settings_get_default().
+// It should only be executed on the UI thread and must be called before
+// GetMimeIcon().
+void DetectGtkTheme();
+#endif
+
 // Gets the file name for an icon given the mime type and icon pixel size.
 // Where an icon is a square image of |size| x |size|.
 // This will try to find the closest matching icon. If that's not available,