Add a histogram tracking toggling the focus highlight preference

Bug: 1075862
Change-Id: I5da5ee8984896e5c39baef36c06f46eb451524bd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2327363Reviewed-by: dpapad <dpapad@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Commit-Queue: Alice Boxhall <aboxhall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#817322}

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

@@ -37,6 +37,7 @@
             class="hr"
             hidden$="[[!showFocusHighlightOption_]]"
             pref="{{prefs.settings.a11y.focus_highlight}}"
+            on-setting-boolean-control-change="onFocusHighlightChange_"
             label="$i18n{focusHighlightLabel}">
         </settings-toggle-button>
         <settings-toggle-button

chrome/browser/resources/settings/a11y_page/a11y_page.js

@@ -198,6 +198,15 @@ Polymer({
   onEnableLiveCaptionSubtitleChanged_(enableLiveCaptionSubtitle) {
     this.enableLiveCaptionSubtitle_ = enableLiveCaptionSubtitle;
   },
+
+  /**
+   * @private
+   * @param {!Event} event
+   */
+  onFocusHighlightChange_(event) {
+    chrome.metricsPrivate.recordBoolean(
+        'Accessibility.FocusHighlight.ToggleEnabled', event.target.checked);
+  },
   // </if>
 
   // <if expr="chromeos">

tools/metrics/histograms/histograms_xml/accessibility/histograms.xml

@@ -424,6 +424,17 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   </summary>
 </histogram>
 
+<histogram name="Accessibility.FocusHighlight.ToggleEnabled"
+    enum="BooleanEnabled" expires_after="2021-03-31">
+  <owner>aboxhall@chromium.org</owner>
+  <owner>chrome-a11y-core@google.com</owner>
+  <summary>
+    The value of the &quot;show a quick focus highlight&quot; setting, logged
+    immediately after toggling. This will show us how often users are turning
+    the feature on, and how often they are turning it back off again.
+  </summary>
+</histogram>
+
 <histogram name="Accessibility.ImageLabels" enum="BooleanEnabled"
     expires_after="M89">
   <owner>katie@chromium.org</owner>