[MD settings] adjusting heights of settings rows; removing two .css files; unifying settings layout

chrome/browser/resources/settings/a11y_page/a11y_page.html

 <link rel="import" href="chrome://resources/polymer/v1_0/polymer/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-button/paper-button.html">
 <link rel="import" href="chrome://md-settings/controls/settings_checkbox.html">
 
 <dom-module id="settings-a11y-page">
   <link rel="import" type="css" href="chrome://md-settings/settings_shared.css">
   <template>
     <div class="settings-box row first">
       <span i18n-content="a11yExplanation"></span>
       <a i18n-values="href:a11yLearnMoreUrl" i18n-content="learnMore"
           target="_blank"></a>
     </div>
 
-    <div class="settings-box">
+    <div class="settings-box block">
       <settings-checkbox i18n-values="label:optionsInMenuLabel"
           pref="{{prefs.settings.a11y.enable_menu}}">
       </settings-checkbox>
       <settings-checkbox i18n-values="label:largeMouseCursorLabel"
           pref="{{prefs.settings.a11y.large_cursor_enabled}}">
       </settings-checkbox>
       <settings-checkbox i18n-values="label:highContrastLabel"
           pref="{{prefs.settings.a11y.high_contrast_enabled}}">
       </settings-checkbox>
       <settings-checkbox
@@ skipping 39 matching lines @@
 
     <div class="settings-box">
       <div class="button-strip">
         <paper-button i18n-content="moreFeaturesLink"
             on-tap="onMoreFeaturesTap_"></paper-button>
       </div>
     </div>
   </template>
   <script src="a11y_page.js"></script>
 </dom-module>