[Switch Access] Fix dialog height growing when prompt changes

AX-Relnotes: N/A
Fixed: 1155744
Change-Id: Ib0c63e0518b8f7fcfc5f467c76dd95d34430acf4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2574785
Auto-Submit: Josiah Krutz <josiahk@google.com>
Reviewed-by: Jimmy Gong <jimmyxgong@chromium.org>
Commit-Queue: Josiah Krutz <josiahk@google.com>
Cr-Commit-Position: refs/heads/master@{#833965}

chrome/browser/resources/settings/chromeos/os_a11y_page/switch_access_action_assignment_dialog.html

@@ -16,6 +16,10 @@
         width: 420px;
       }
 
+      #prompt {
+        height: 40px;
+      }
+
       #switchAssignments {
         background-color: var(--google-grey-refresh-100);
         border-radius: 4px;
@@ -39,7 +43,7 @@
     <cr-dialog id="switchAccessActionAssignmentDialog" show-on-attach>
       <div slot="title">[[dialogTitle_]]</div>
       <div slot="body">
-        <div aria-live="polite">
+        <div id="prompt" aria-live="polite">
           [[promptText_]]
         </div>
         <div id="switchAssignments">