[gtk] (3 commits) Non-fast-forward update to branch wip/matthiasc/shared-glyph-cache

[Matthias Clasen <matthiasc src gnome org>]

The branch 'wip/matthiasc/shared-glyph-cache' was changed in a way that was not a fast-forward update.
NOTE: This may cause problems for people pulling from the branch. For more information,
please see:

 https://wiki.gnome.org/Git/Help/NonFastForward

Commits removed from the branch:

  1c47d86... Attempt to share the glyph cache
  c77cede... More hackery
  e4d9796... Fix an off-by-one error
  5471eb0... icon cache: Avoid a double free
  09ce4f6... Move shared context creation to the frontend
  42e2c68... Cleanups
  86023b0... Make the icon cache shared too
  6aa3b74... Reinstate some debug output
  f298b2a... gl: Add some debug annotation to icon cache
  b19450b... Do away with all the context switching
  6c3154d... Move towards a unified cache
  dc7076f... Consider all offscreen drawings for the icon cache

Commits added to the branch:

  d8f22ab... gdk: Create a global shared GL context
  0dd5948... Share glyph and icon caches
  66f67f2... Consider all offscreen drawings for the icon cache