Roll src/third_party/skia 5f1692c60a43..18df87ec8bda (12 commits) (#7368)

https://skia.googlesource.com/skia.git/%2Blog/5f1692c60a43..18df87ec8bda

git log 5f1692c60a43bfb9f9039e288862c82a9f7cbc8e..18df87ec8bda0d01999c52fde7c1b7eed663afb5 --date=short --no-merges --format=%ad %ae %s
2019-01-04 brianosman@google.com Fix bugs and add features to imgcvt
2019-01-04 recipe-roller@chromium.org Roll recipe dependencies (trivial).
2019-01-04 reed@google.com remove blob iterator::applyFontToPaint
2019-01-04 egdaniel@google.com Set skia_use_vulkan on our vulkan bots.
2019-01-04 reed@google.com start to change Viewer's filtering to know about fonts
2019-01-04 kjlubick@google.com more extra semis
2019-01-03 egdaniel@google.com Add support to gpu command buffers to wrap an external command buffer.
2019-01-04 jcgregorio@google.com Fix link in /dev/contrib.
2019-01-04 michaelludwig@google.com Revert "Use specialized quad lists in rectangle ops"
2019-01-03 brianosman@google.com Add SkColorSpace factory from 3x3 row-major gamut and transfer function
2019-01-04 kjlubick@google.com remove more extra semicolons
2019-01-03 egdaniel@google.com Restrict ops that can be executed when we have a wrapped vulkan secondary command buffer.

The AutoRoll server is located here: https://autoroll.skia.org/r/skia-flutter-autoroll

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

If the roll is causing failures, please contact the current sheriff (bungeman@google.com), and stop
the roller if necessary.

DEPS

@@ -23,7 +23,7 @@ vars = {
   'fuchsia_git': 'https://fuchsia.googlesource.com',
   'github_git': 'https://github.com',
   'skia_git': 'https://skia.googlesource.com',
-  'skia_revision': '5f1692c60a43bfb9f9039e288862c82a9f7cbc8e',
+  'skia_revision': '18df87ec8bda0d01999c52fde7c1b7eed663afb5',
 
   # When updating the Dart revision, ensure that all entries that are
   # dependencies of Dart are also updated to match the entries in the

ci/licenses_golden/licenses_skia

-Signature: 655297dc012182697fdde2be7116726e
+Signature: 13af94568cbb99455e1d647a9015e2a7
 
 UNUSED LICENSES: