[cairo] Performance degradation of font cache in 1.11.3

[Chris Wilson]

Hmm, I hit the same performance regression recently when comparing
cairo-1.10 and the soon-to-be cairo-1.12:

commit da381da7f324497132ca547246c5299708fb968e
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Tue Feb 28 14:50:16 2012 +0000

    scaled-font: Key the cache on the original font face
    
    Complete the task started in cd4b2d843b2a8c06ba78c15ff65763b5bdf54dc6 by
    remembering to compute the insertion hash on the original font face as
    well as the lookup hashes. Also take advantage by deferring resolution
    of the implementation for the font face until after we fail to find an
    already constructed scaled font.
    
    Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>

Fixes the performance regression for me.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre