[gtk] (15 commits) ...Merge branch 'wip/chergert/opbuffer' into 'master'

[Matthias Clasen <matthiasc src gnome org>]

Summary of changes:

  a00d12c... prototype OpBuffer helper for building op buffer (*)
  571068a... Drop OP_CHANGE_VAO (*)
  58d57e1... gl: Drop buffer_size (*)
  97f3371... gl: avoid calculating vertex_data until necessary (*)
  b53fa48... Fix load_vertex_data (*)
  49748c9... Some more vertex data reshuffling (*)
  c5af463... Cache glyph textures in render nodes (*)
  e34d1b8... gl: Slightly rework the icon cache api (*)
  dd5ee87... gl: Speed up icon cache lookups (*)
  7197743... pixbuf utils: Preserve format information (*)
  be13a23... icon theme: Avoid mime sniffing (*)
  0895f02... icon theme: Avoid a string copy (*)
  173bb2e... gsk: Fix uninitialized memory (*)
  d777300... Fix a crash with glyph caching (*)
  6c92b82... Merge branch 'wip/chergert/opbuffer' into 'master'

(*) This commit already existed in another branch; no separate mail sent