MD Settings: Add feature flag for showing content settings in a per-origin view.

chrome/browser/flag_descriptions.h

Index: chrome/browser/flag_descriptions.h
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index dba02b38595c96dce6d29324df07878a9c0bc391..464b7829fa7b39a3fbdb3736cb3e196c490b7c93 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -260,6 +260,13 @@ extern const char kTopChromeMdMaterial[];
 // Top Chrome material hybrid design option (for touchscreens).
 extern const char kTopChromeMdMaterialHybrid[];
 
+// Title of the flag which enables site details in MD settings.
+extern const char kSiteDetails[];
+
+// Description of the flag which enables or disables site details in MD
+// settings.
+extern const char kSiteDetailsDescription[];
+
 // Title of the flag which enables the site settings all sites list and site
 // details.
 extern const char kSiteSettings[];