UI: Match 'Depends-on' text color to core change metadata items

To improve consistency, also add a tool tip.

Screenshots: https://imgur.com/a/wEXgeMU

Change-Id: Iba0d5b1e06ce1a74a8e95acc09c6f628d070d0e0

gr-depends-on-plugin/gr-depends-on-plugin_html.js

diff --git a/gr-depends-on-plugin/gr-depends-on-plugin_html.js b/gr-depends-on-plugin/gr-depends-on-plugin_html.js
index fbdc59d..3dd5a53 100644
--- a/gr-depends-on-plugin/gr-depends-on-plugin_html.js
+++ b/gr-depends-on-plugin/gr-depends-on-plugin_html.js
@@ -33,6 +33,7 @@
       --iron-icon-width: 18px;
     }
     .title {
+      color: var(--deemphasized-text-color);
       display: table-cell;
       vertical-align: top;
       max-width: 20em;
@@ -56,7 +57,14 @@
   </style>
   <div class="depends_on_block">
     <section>
-      <span class="title">Depends-on</span>
+      <span class="title">
+        <gr-tooltip-content
+          has-tooltip
+          title="List of changes that the current change depends on."
+        >
+          Depends-on
+        </gr-tooltip-content>
+      </span>
       <span class="value">
         <span hidden$="[[!_isPending]]">loading...</span>
         <span hidden$="[[_isPending]]">