[MD settings] icon color and sizing centralized

chrome/browser/resources/settings/settings_menu/settings_menu.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-icon/iron-icon.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-icons/device-icons.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-icons/hardware-icons.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-icons/iron-icons.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-icons/social-icons.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-menu/paper-menu.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-menu/paper-submenu.html">
+<link rel="import" href="chrome://md-settings/settings_shared_css.html">
 
 <if expr="chromeos">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-icons/device-icons.html">
 </if>
 
 <dom-module id="settings-menu">
   <template>
-    <style>
+    <style include="settings-shared">
       iron-icon {
+        --iron-icon-fill-color: var(--settings-side-nav-color);
+        --iron-icon-stroke-color: var(--settings-side-nav-color);
         -webkit-margin-end: 16px;
-        height: 20px;
-        width: 20px;
       }
 
       .menu-trigger span {
         -webkit-margin-end: 16px;
         flex: 1;
       }
 
       paper-menu {
-        background-color: rgb(236, 239, 241);
-        color: #5a5a5a;
+        background-color: var(--settings-background-color);
+        color: var(--settings-side-nav-color);
         font-size: 13px;
         --paper-menu-selected-item: {
           font-weight: 500;
         };
         --paper-menu-focused-item-after: {
           background: none;
         };
       }
 
       paper-submenu {
         --paper-menu-selected-item: {
           font-weight: 500;
         };
       }
 
       paper-submenu paper-menu {
         --paper-menu-selected-item: {
-          color: #4285f4;
+          color: var(--google-blue-500);
           font-weight: 500;
         };
         padding: 0;
       }
 
       paper-submenu div {
         @apply(--layout-center);
         -webkit-margin-start: 24px;
         display: flex;
         font-size: 13px;
@@ skipping 99 matching lines @@
       </paper-submenu>
       <paper-submenu on-tap="openPage_">
         <div class="menu-trigger">
           <span i18n-content="aboutProgram"></span>
         </div>
       </paper-submenu>
     </paper-menu>
   </template>
   <script src="settings_menu.js"></script>
 </dom-module>