[WebUI][Settings] Add customized behaviors description string

Add description text to the customized behaviors section for content
settings in chrome://settings/content.

Bug: 1113642
Change-Id: Idb8dd03d152f8c2bdccc27dffca1bdc8e233aca7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2555037Reviewed-by: dpapad <dpapad@chromium.org>
Commit-Queue: Sean Harrison <harrisonsean@chromium.org>
Cr-Commit-Position: refs/heads/master@{#830512}

chrome/app/settings_strings.grdp

@@ -1677,6 +1677,9 @@
   <message name="IDS_SETTINGS_SITE_SETTINGS_CUSTOMIZED_BEHAVIORS" desc="Label for the site settings exceptions.">
     Customized behaviors
   </message>
+  <message name="IDS_SETTINGS_SITE_SETTINGS_CUSTOMIZED_BEHAVIORS_DESCRIPTION" desc="Description for the site settings exceptions.">
+    Sites listed below follow a custom setting instead of the default
+  </message>
   <message name="IDS_SETTINGS_SITE_SETTINGS_ADS_DESCRIPTION" desc="Description of the ads content setting.">
     Sites usually show ads so they can provide content or services for free. But, some sites are known to show intrusive or misleading ads.
   </message>

chrome/app/settings_strings_grdp/IDS_SETTINGS_SITE_SETTINGS_CUSTOMIZED_BEHAVIORS_DESCRIPTION.png.sha1

+c389010d57a048d2b9cf09eb090cf81284ef1bb6
\ No newline at end of file

chrome/browser/resources/settings/site_settings/category_setting_exceptions.html

@@ -5,6 +5,9 @@
     </style>
     <div id="exceptionHeader" hidden="[[!enableContentSettingsRedesign_]]">
       <h2>$i18n{siteSettingsCustomizedBehaviors}</h2>
+      <div id="exceptionHeaderSubLabel" class="secondary">
+        $i18n{siteSettingsCustomizedBehaviorsDescription}
+      </div>
     </div>
     <site-list
         has-discarded-exceptions="{{blockSiteListHasDiscardedExceptions_}}"

chrome/browser/ui/webui/settings/settings_localized_strings_provider.cc

@@ -1948,6 +1948,8 @@ void AddSiteSettingsStrings(content::WebUIDataSource* html_source,
      IDS_SETTINGS_SITE_SETTINGS_DEFAULT_BEHAVIOR_DESCRIPTION},
     {"siteSettingsCustomizedBehaviors",
      IDS_SETTINGS_SITE_SETTINGS_CUSTOMIZED_BEHAVIORS},
+    {"siteSettingsCustomizedBehaviorsDescription",
+     IDS_SETTINGS_SITE_SETTINGS_CUSTOMIZED_BEHAVIORS_DESCRIPTION},
     {"siteSettingsAdsDescription", IDS_SETTINGS_SITE_SETTINGS_ADS_DESCRIPTION},
     {"siteSettingsAdsAllowed", IDS_SETTINGS_SITE_SETTINGS_ADS_ALLOWED},
     {"siteSettingsAdsBlocked", IDS_SETTINGS_SITE_SETTINGS_ADS_BLOCKED},