Add experimental support for enterKeyHint.

enterKeyHint allows customization of the virtual keyboard enter
key. Enabled behind a flag since it isn't approved to ship yet.

Spec:
https://github.com/whatwg/html/pull/3538

BUG=634330

Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_layout_ng
Change-Id: I32b510d8157e0c676300a38bb4c7fa2bbced0b3d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1221696
Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Reviewed-by: Changwan Ryu <changwan@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Reviewed-by: Ken Buchanan <kenrb@chromium.org>
Reviewed-by: Joshua Bell <jsbell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661904}
48 files changed