[css-navigation-1] Add stub definitions for @navigation (phase: loading | ready | committed).

Author: dbaron

css-navigation-1/Overview.bs

@@ -319,7 +319,8 @@ with <<navigation-condition>> defined as:
 <dfn><<navigation-in-parens>></dfn> = ( <<navigation-condition>> ) | ( <<navigation-test>> ) | <<general-enclosed>>
 <dfn><<navigation-test>></dfn> = <<navigation-location-test>> |
                     <<navigation-location-between-test>> |
-                    <<navigation-type-test>>
+                    <<navigation-type-test>> |
+                    <<navigation-phase-test>>
 
 <dfn><<navigation-location-test>></dfn> = <<navigation-location-keyword>> : <<route-location>>
 <dfn><<navigation-location-keyword>></dfn> = at | with | from | to
@@ -329,6 +330,9 @@ with <<navigation-condition>> defined as:
 
 <dfn><<navigation-type-test>></dfn> = history : <<navigation-type-keyword>>
 <dfn><<navigation-type-keyword>></dfn> = traverse | back | forward | reload
+
+<dfn><<navigation-phase-test>></dfn> = phase : <<navigation-phase-keyword>>
+<dfn><<navigation-phase-keyword>></dfn> = loading | ready | committed
 </pre>
 
 ISSUE: Should we use ''at''/''with''/''from''/''to'' or ''current''/''other''/''from''/''to''?
@@ -406,6 +410,16 @@ as follows:
     : history: reload
     :: True if the [=current navigation type=] is {{NavigationType/reload}}.
 
+: <<navigation-phase-test>>
+::    : phase: loading
+    :: ISSUE: Needs to be defined.
+    : phase: ready
+    :: ISSUE: Needs to be defined.
+
+        NOTE: Only applies to cross-document navigations.
+    : phase: committed
+    :: ISSUE: Needs to be defined.
+
 : <<general-enclosed>>
 ::
     The result is false.