[CrOS MultiDevice] Format single host device case in Setup Flow

The specs for this case are in Comment 13 in the bug:
https://bugs.chromium.org/p/chromium/issues/detail?id=878644#c13

Screenshot of results of CL: http://screen/KJj4Rxeo84H

Note that the font size (13px) and line height (16px) are explicitly
spelled out here because the default height without that specification
was slightly off.

Bug: 878644
Change-Id: Ie93a3c173c3b43b7cab23177a02c8eb8f9c70181
Reviewed-on: https://chromium-review.googlesource.com/1247194
Commit-Queue: Jordy Greenblatt <jordynass@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#594579}

ui/webui/resources/cr_components/chromeos/multidevice_setup/multidevice_setup.html

@@ -19,7 +19,9 @@
         @apply --layout-vertical;
         box-sizing: border-box;
         color: var(--google-grey-700);
+        font-size: 13px;
         height: 100%;
+        line-height: 16px;
         margin: auto;
         max-height: 640px;
         max-width: 768px;

ui/webui/resources/cr_components/chromeos/multidevice_setup/start_setup_page.html

@@ -15,6 +15,11 @@
         margin-top: 48px;
       }
 
+      #singleDeviceName {
+        color: var(--google-grey-900);
+        margin-top: 16px;
+      }
+
       #deviceDropdown {
         margin-top: 16px;
       }
@@ -74,7 +79,8 @@
           <div id="deviceSelectionContainer" class="flex">
             [[getDeviceSelectionHeader_(devices)]]
             <div class="flex"></div>
-            <div hidden$="[[!doesDeviceListHaveOneElement_(devices)]]">
+            <div id="singleDeviceName"
+                hidden$="[[!doesDeviceListHaveOneElement_(devices)]]">
               [[getFirstDeviceNameInList_(devices)]]
             </div>
             <div hidden$="[[!doesDeviceListHaveMultipleElements_(devices)]]">