[MD settings] move the subpage search underline up

This CL moves the underline in the subpage search up by two px, to match
mocks (request by Alan).

BUG=638453
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2321733002
Cr-Commit-Position: refs/heads/master@{#417319}

chrome/browser/resources/settings/settings_page/settings_subpage_search.html

@@ -9,6 +9,18 @@
   <template>
     <style>
       :host {
+        --subpage-search-underline: {
+          margin-bottom: -2px;
+          margin-top: -2px;
+        }
+      }
+
+      :host {
+        --paper-input-container-underline: var(--subpage-search-underline);
+        --paper-input-container-underline-focus:
+            var(--subpage-search-underline);
+        --paper-input-container-underline-disabled:
+            var(--subpage-search-underline);
         --paper-input-suffix: {
           /* Required to align the icon in |clearSearch| vertically. */
           line-height: 0;