[MD-Settings] Make section titles into <h2> headings for a11y.

chrome/browser/resources/settings/settings_page/settings_section.html

Index: chrome/browser/resources/settings/settings_page/settings_section.html
diff --git a/chrome/browser/resources/settings/settings_page/settings_section.html b/chrome/browser/resources/settings/settings_page/settings_section.html
index 604547432070dd7c480cf3f0e8129d4fc5c66d70..353f1964cb2ea0f0667473b90534776d9cf73af0 100644
--- a/chrome/browser/resources/settings/settings_page/settings_section.html
+++ b/chrome/browser/resources/settings/settings_page/settings_section.html
@@ -18,6 +18,10 @@
         margin-bottom: 12px;
       }
 
+      .title {
+        margin-bottom: 0;

[Dan Beam, 2016/08/31 18:43:41]

nit: just put this in #header .title below

[hcarmona, 2016/08/31 19:07:49]

Done.

+      }
+
       #header .title {
         color: var(--paper-grey-600);
         font-size: 13px;
@@ -54,7 +58,7 @@
       }
     </style>
     <div id="header">
-      <div class="title">{{pageTitle}}</div>
+      <h2 class="title">{{pageTitle}}</h2>
     </div>
     <div id="card">
       <content id="content"></content>