xkb: Fallback to DOM|code|->keyboard code mapping

If XkbLookup fails and there is no DOM|code|->DOM|key| mapping. This
will happen in cases where a DOM|code| exists without a W3C standard
DOM|key|.

BUG=952051
TBR=wez

Change-Id: I63af869118e15c99bcb7cd4cbcb3e58def610334
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2008049Reviewed-by: Jesse Schettler <jschettler@chromium.org>
Commit-Queue: Jesse Schettler <jschettler@chromium.org>
Auto-Submit: Mathew King <mathewk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#732934}

ui/events/ozone/layout/xkb/xkb_keyboard_layout_engine.cc

@@ -747,7 +747,13 @@ bool XkbKeyboardLayoutEngine::Lookup(DomCode dom_code,
     // If we do not have matching legacy Xkb keycode for the Dom code,
     // we could be dealing with a newer application launcher or similar
     // key. Let's see if we have a basic mapping for it.
-    return DomCodeToNonPrintableDomKey(dom_code, dom_key, key_code);
+    if (!DomCodeToNonPrintableDomKey(dom_code, dom_key, key_code)) {
+      // If no Dom Key was found see if there is a matching Dom Code to keycode
+      // mapping for it.
+      *dom_key = DomKey::UNIDENTIFIED;
+      *key_code = DomCodeToUsLayoutNonLocatedKeyboardCode(dom_code);
+    }
+    return true;
   }
 
   // Classify the keysym and convert to DOM and VKEY representations.