Add DataApiManager field stale flag

This will allow it to know when a request needs to be re-made at a later
time.

* src/dapi/DataApiManager (fieldStale, isFieldStale): Added
(fieldNotReady): Check stale status of field

src/dapi/DataApiManager.js

@@ -85,6 +85,12 @@ module.exports = Class( 'DataApiManager' )
      */
     'private _fieldApiTimer': 0,
 
+    /**
+     * Fields that require API requests
+     * @type {Object}}
+     */
+    'private _fieldStale': {},
+
     /**
      * API descriptions
      * @type {Object}
@@ -200,6 +206,9 @@ module.exports = Class( 'DataApiManager' )
             }
         };
 
+        // field is about to be re-loaded
+        this.fieldStale( name, index, false );
+
         this._setFieldApiTimer();
         return this;
     },
@@ -221,6 +230,43 @@ module.exports = Class( 'DataApiManager' )
     },
 
 
+    /**
+     * Marks field for re-loading
+     *
+     * Stale fields will not be considered to have data, but the data
+     * will remain in memory until the next request.
+     *
+     * @param {string}   field field name
+     * @param {number}   index field index
+     * @param {?boolean} stale whether field is stale
+     *
+     * @return {DataApiManager} self
+     */
+    'public fieldStale': function( field, index, stale )
+    {
+        stale = ( stale === undefined ) ? true : !!stale;
+
+        this._fieldStale[ field ]          = this.fieldStale[ field ] || [];
+        this._fieldStale[ field ][ index ] = stale;
+
+        return this;
+    },
+
+
+    /**
+     * Whether field is marked stale
+     *
+     * @param {string} field field name
+     * @param {number} index field index
+     *
+     * @return {boolean} whether field is stale
+     */
+    'protected isFieldStale': function( field, index )
+    {
+        return ( this._fieldStale[ field ] || [] )[ index ] === true;
+    },
+
+
     'public fieldNotReady': function( id, i, bucket )
     {
         if ( !( this.hasFieldData( id, i ) ) )
@@ -437,6 +483,11 @@ module.exports = Class( 'DataApiManager' )
         // default to "combined" index of -1 if no index is provided
         index = ( index === undefined ) ? -1 : +index;
 
+        if ( this.isFieldStale( name, index ) )
+        {
+            return false;
+        }
+
         return ( ( this._fieldData[ name ] || {} )[ index ] )
             ? true
             : false;