MD Settings: Add description for Protected Content

chrome/app/settings_strings.grdp

Index: chrome/app/settings_strings.grdp
diff --git a/chrome/app/settings_strings.grdp b/chrome/app/settings_strings.grdp
index 052a8b40f53a7062e989be91793387a0264989c5..4819539a537da3c12c7e924debab665f3374c2cb 100644
--- a/chrome/app/settings_strings.grdp
+++ b/chrome/app/settings_strings.grdp
@@ -1756,6 +1756,9 @@
   <message name="IDS_SETTINGS_SITE_SETTINGS_PROTECTED_CONTENT" desc="Label for the protected content site settings.">
     Protected Content
   </message>
+  <message name="IDS_SETTINGS_SITE_SETTINGS_PROTECTED_CONTENT_EXPLANATION" desc="Text that is displayed on the Protected Content section of Content Settings. This text explains that enabling protected content may require using a uniquely identifiable machine identifier.">
+    Some content services use unique identifiers for the purposes of authorizing access to protected content.
+  </message>
   <message name="IDS_SETTINGS_SITE_SETTINGS_PROTECTED_CONTENT_ENABLE" desc="Label for the toggle enabling protected content.">
     Allow identifiers for protected content (computer restart may be required)
   </message>