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}
diff --git a/html/dom/elements-misc.js b/html/dom/elements-misc.js
index df415ae..b747ac6 100644
--- a/html/dom/elements-misc.js
+++ b/html/dom/elements-misc.js
@@ -53,6 +53,7 @@
 
   // Global attributes should exist even on unknown elements
   undefinedelement: {
+    enterKeyHint: {type: "enum", keywords: ["enter", "done", "go", "next", "previous", "search", "send"]},
     inputMode: {type: "enum", keywords: ["none", "text", "tel", "url", "email", "numeric", "decimal", "search"]},
   },
 };
diff --git a/html/semantics/forms/attributes-common-to-form-controls/contains.json b/html/semantics/forms/attributes-common-to-form-controls/contains.json
index 357a1e6..62326d3 100644
--- a/html/semantics/forms/attributes-common-to-form-controls/contains.json
+++ b/html/semantics/forms/attributes-common-to-form-controls/contains.json
@@ -24,6 +24,10 @@
         "original_id": "autofocusing-a-form-control:-the-autofocus-attribute"
     },
     {
+        "id": "input-modalities-the-enterkeyhint-attribute",
+        "original_id": "input-modalities:-the-enterkeyhint-attribute"
+    },
+    {
         "id": "input-modalities-the-inputmode-attribute",
         "original_id": "input-modalities:-the-inputmode-attribute"
     },
@@ -31,4 +35,4 @@
         "id": "autofilling-form-controls-the-autocomplete-attribute",
         "original_id": "autofilling-form-controls:-the-autocomplete-attribute"
     }
-]
\ No newline at end of file
+]