Loading icons is quite slow because we need to stat many files in many directories.
That's why gtk adds a cache in the icon theme directory so it avoids stating lots
of files.
The cache file can be generated with gtk-update-icon-cache utility on a theme
directory. If the cache is not present, corrupted, or outdated, the normal slow lookup
is still run.
[ChangeLog][QtGui][QIcon] fromTheme gained the ability to use the GTK icon cache
to speed up lookups.
Change-Id: I3ab8a9910be67a34034556023be61a86789a7893
Reviewed-by: David Faure <david.faure@kdab.com>
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