[gtk] (7 commits) Non-fast-forward update to branch matthiasc/for-master

[Matthias Clasen <matthiasc src gnome org>]

The branch 'matthiasc/for-master' 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:

  de24b4f... cssshadowvalue: Add a parsing function
  9770872... css: Implement the drop-shadow filter
  a1f7073... Add tests for the css filter property
  6e84a8c... Adjust docs
  a15e1e2... css: Fix blur filter interpretation
  9abebb5... cssfiltervalue: Reject invalid filters
  4d84612... Add more css filter parser tests
  37751c1... fixup! cssshadowvalue: Add a parsing function
  50e81c1... fixup! Add more css filter parser tests

Commits added to the branch:

  92ddc7a... cssshadowvalue: Add gtk_css_shadow_value_pop_snapshot
  adadf7d... cssshadowvalue: Add a parsing function
  c4450ce... cssshadowvalue: Add a 'filter mode'
  dfecca4... cssfiltervalue: Implement drop-shadows
  efb6789... cssfiltervalue: Fix blur filter interpretation
  0acc728... cssfiltervalue: Reject invalid filters
  1a6c747... Add tests for the css filter property