[gtk] (18 commits) ...Merge branch 'wip/baedert/for-master' into 'master'

[Matthias Clasen <matthiasc src gnome org>]

Summary of changes:

  d6b3ac8... testsuite: Fix test case indentation (*)
  34008e6... gl renderer: Ignore rounded clip that only increase the cli (*)
  46bb3e3... icontheme: Indentation (*)
  4e42074... adwaita: Remove header bar border radius (*)
  339d9f0... gl renderer: Remove unused flag (*)
  6a60b0f... gl renderer: Try to intersect rounded clips more often (*)
  6cde640... gl renderer: Remove outdated comment (*)
  37d7ab8... gl renderer: Avoid 9-slicing things that can't be (*)
  11f07cb... GdkRGBA: Fix typo in documentation (*)
  f721d2d... debug: Remove resize highlighting (*)
  720c298... snapshot: Use collect_default directoy in push_debug() (*)
  f678b38... widget: Remove useless if statement (*)
  14589c2... widget: Save a gtk_css_node_get_style call (*)
  de0547e... migration guide: Remove a stray html tag (*)
  2bd87ce... boxlayout: Remove unused include (*)
  c1f5153... boxlayout: Remove unnecessary checks (*)
  7e19911... testwidgettransforms: Fix GtkBox casts (*)
  8611faf... Merge branch 'wip/baedert/for-master' into 'master'

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