Add a enhanceTextSelection preference to the viewer

extensions/chromium/preferences_schema.json

@@ -94,6 +94,10 @@
       "type": "boolean",
       "description": "Whether to prevent the extension from reporting the extension and browser version to the extension developers.",
       "default": false
+    },
+    "enhanceTextSelection": {
+      "type": "boolean",
+      "default": false
     }
   }
 }