MD Settings: Fix several global UI polish bugs.

chrome/browser/resources/settings/settings_ui/settings_ui.html

 <link rel="import" href="chrome://resources/cr_elements/cr_drawer/cr_drawer.html">
 <link rel="import" href="chrome://resources/cr_elements/cr_toolbar/cr_toolbar.html">
 <link rel="import" href="chrome://resources/cr_elements/icons.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-flex-layout/iron-flex-layout.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-header-panel/paper-header-panel.html">
 <link rel="import" href="/direction_delegate.html">
 <link rel="import" href="/global_scroll_target_behavior.html">
 <link rel="import" href="/i18n_setup.html">
 <link rel="import" href="/icons.html">
@@ skipping 15 matching lines @@
         @apply(--layout-fit);
         --paper-header-panel-waterfall-container: {
           overflow-x: auto;  /* Undo paper-header-panel default of 'hidden'. */
           overflow-y: overlay;
         };
         -webkit-user-select: none;
         background-color: var(--settings-background-color);
         color: var(--paper-grey-800);
         display: flex;
         flex-direction: column;
+        line-height: 154%; /* Apply 20px line-height to all texts by default. */
         overflow: hidden;  /* Prevent double scroll bar bugs. */
       }
 
       paper-header-panel {
         flex: 1;
       }
 
       .paper-header {
         -webkit-padding-start: 24px;
         align-items: center;
@@ skipping 49 matching lines @@
       <settings-main id="main" prefs="{{prefs}}"
           toolbar-spinner-active="{{toolbarSpinnerActive_}}"
           page-visibility="[[pageVisibility_]]"
           show-android-apps="[[showAndroidApps_]]"
           advanced-toggle-expanded="{{advancedOpened_}}">
       </settings-main>
     </paper-header-panel>
   </template>
   <script src="settings_ui.js"></script>
 </dom-module>