Update the WebUI certificate viewer dialog's headers' aria role.

This change updates the headers' aria role to be 'heading' instead of
'group', which is a more appropriate role given the definitions from w3.
This also improves screen readers' understanding of these text blocks.

Bug: 1116623
Change-Id: Iac4fa60c72da8a130bd28841889a3826a755c8e7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2357461Reviewed-by: dpapad <dpapad@chromium.org>
Commit-Queue: Cliff Smolinsky <cliffsmo@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#798831}

chrome/browser/resources/certificate_viewer.html

@@ -32,13 +32,13 @@
         <!-- General -->
         <tabpanel id="general" aria-labelledby="general-tab">
           <!-- Usages -->
-          <h3 id="usages-title" role="group">$i18n{usages}</h3>
+          <h3 id="usages-title" role="heading">$i18n{usages}</h3>
           <div id="usages"></div>
 
           <div class="groups">
             <!-- Issued to -->
             <div>
-              <h3 role="group">$i18n{issuedTo}</h3>
+              <h3 role="heading">$i18n{issuedTo}</h3>
             </div>
             <div>
               <div class="attribute">$i18n{cn}</div>
@@ -55,7 +55,7 @@
 
             <!-- Issued by -->
             <div>
-              <h3 role="group">$i18n{issuedBy}</h3>
+              <h3 role="heading">$i18n{issuedBy}</h3>
             </div>
             <div>
               <div class="attribute">$i18n{cn}</div>
@@ -72,7 +72,7 @@
 
             <!-- Validity -->
             <div>
-              <h3 role="group">$i18n{validity}</h3>
+              <h3 role="heading">$i18n{validity}</h3>
             </div>
             <div>
               <div class="attribute">$i18n{issuedOn}</div>
@@ -85,7 +85,7 @@
 
             <!-- Fingerprints -->
             <div>
-              <h3 role="group">$i18n{fingerprints}</h3>
+              <h3 role="heading">$i18n{fingerprints}</h3>
             </div>
             <div>
               <div class="attribute">$i18n{sha256}</div>
@@ -101,19 +101,19 @@
         <!-- Details -->
         <tabpanel id="details" aria-labelledby="details-tab">
           <div id="hierarchy-section" class="vertical-box">
-            <h3 id="hierarchy-label" role="group">$i18n{hierarchy}</h3>
+            <h3 id="hierarchy-label" role="heading">$i18n{hierarchy}</h3>
             <tree id="hierarchy" class="section-contents"
                   aria-labelledby="hierarchy-label"
                   icon-visibility='hidden'></tree>
           </div>
           <div id="cert-fields-section" class="vertical-box">
-            <h3 id="cert-fields-label" role="group">$i18n{certFields}</h3>
+            <h3 id="cert-fields-label" role="heading">$i18n{certFields}</h3>
             <tree id="cert-fields" class="section-contents"
                   aria-labelledby="cert-fields-label"
                   icon-visibility='hidden'></tree>
           </div>
           <div id="cert-field-value-section" class="vertical-box">
-            <h3 id="cert-field-value-label" role="group">
+            <h3 id="cert-field-value-label" role="heading">
               $i18n{certFieldVal}
             </h3>
             <div id="cert-field-value" class="section-contents" tabindex="0"