Test fragment scrolling and history restoration interaction w/ scroll anchoring.

third_party/WebKit/Source/build/scripts/templates/InternalRuntimeFlags.idl.tmpl

 {% from "macros.tmpl" import license %}
 {{ license() }}
 
 [
     GarbageCollected,
 ] interface InternalRuntimeFlags {
     {% for feature in standard_features %}
-{#
-    Currently assuming that runtime flags cannot be changed after startup
-    it's possible that some can be and should be conditionally readonly.
-#}
     {%+ if feature.condition %}[Conditional={{feature.condition}}] {% endif -%}
+    {% if feature.settable_from_internals %}
+    attribute boolean {{feature.first_lowered_name}}Enabled;
+    {% else %}
     readonly attribute boolean {{feature.first_lowered_name}}Enabled;
+    {% endif %}
     {% endfor %}
 };