MD-Settings: Adds an a11y label to most toggle buttons.

chrome/browser/resources/settings/internet_page/network_proxy.html

 <link rel="import" href="chrome://resources/cr_elements/cr_dialog/cr_dialog.html">
 <link rel="import" href="chrome://resources/cr_elements/network/cr_onc_types.html">
 <link rel="import" href="chrome://resources/cr_elements/policy/cr_policy_network_behavior.html">
 <link rel="import" href="chrome://resources/cr_elements/policy/cr_policy_network_indicator.html">
 <link rel="import" href="chrome://resources/html/i18n_behavior.html">
 <link rel="import" href="chrome://resources/html/md_select_css.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-a11y-keys/iron-a11y-keys.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-button/paper-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-input/paper-input-container.html">
@@ skipping 108 matching lines @@
     <div class="settings-box continuation indent"
         hidden$="[[!matches_(proxy_.Type, ProxySettingsType_.WPAD)]]">
       <div>$i18n{networkSectionWpad}</div>
       <div class="middle flex">[[WPAD_]]</div>
     </div>
 
     <!-- Manual -->
     <div id="proxyDiv" class="settings-box continuation single-column indent"
         hidden$="[[!matches_(proxy_.Type, ProxySettingsType_.MANUAL)]]">
       <div class="flex layout horizontal">
-        <div class="flex">$i18n{networkProxyUseSame}</div>
+        <div id="networkProxyToggleLabel" class="flex">
+          $i18n{networkProxyUseSame}
+        </div>
         <paper-toggle-button checked="{{useSameProxy_}}"
             disabled="[[!isEditable_('Type', networkProperties, editable,
-                useSharedProxies_)]]">
+                useSharedProxies_)]]"
+            aria-labelledby="networkProxyToggleLabel">
         </paper-toggle-button>
       </div>
       <div hidden$="[[!useSameProxy_]]" class="layout vertical">
         <network-proxy-input
             on-proxy-change="onProxyInputChange_"
             editable="[[isEditable_('Manual.HTTPProxy.Host', networkProperties,
                 editable, useSharedProxies_)]]"
             value="{{proxy_.Manual.HTTPProxy}}"
             label="$i18n{networkProxy}">
         </network-proxy-input>
@@ skipping 69 matching lines @@
         </paper-button>
         <paper-button class="action-button"
             on-tap="onAllowSharedDialogConfirm_">
           $i18n{confirm}
         </paper-button>
       </div>
     </dialog>
   </template>
   <script src="network_proxy.js"></script>
 </dom-module>