GitLab

- Add MapTraits to allow serialization of a vector of pairs directly
  into a Mojo map for ui::AXNodeData.
- Update AX browsertest to use Gmock matchers for container comparison.
  This test currently depends on an ordering that is not guaranteed by
  abnything and may unexpectedly break in the future.  Using Gmock makes
  it easier to update at such a point in the future.
- Deserialize attribute maps into a base::flat_map and extract the
  underlying result directly into ui::AXNodeData.

Bug: none
Change-Id: I1db2649312ad1e68a40962e27bd5c97da29cc3fe
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2541745Reviewed-by: David Tseng <dtseng@chromium.org>
Reviewed-by: Alex Gough <ajgo@chromium.org>
Reviewed-by: Ken Rockot <rockot@google.com>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#828966}