Fix documentation that referenced Android classes to reference the dart mechanism instead. (#1256)

Author: slightfoot

packages/cloud_firestore/lib/src/snapshot_metadata.dart

@@ -11,17 +11,17 @@ class SnapshotMetadata {
   /// Whether the snapshot contains the result of local writes that have not yet
   /// been committed to the backend.
   ///
-  /// If your listener has opted into metadata updates (via
-  /// [DocumentListenOptions] or [QueryListenOptions]) you will receive another
+  /// If you called [DocumentReference.snapshots] or [Query.snapshots] with
+  /// `includeMetadataChanges` parameter set to `true` you will receive another
   /// snapshot with `hasPendingWrites` equal to `false` once the writes have been
   /// committed to the backend.
   final bool hasPendingWrites;
 
   /// Whether the snapshot was created from cached data rather than guaranteed
   /// up-to-date server data.
   ///
-  /// If your listener has opted into metadata updates (via
-  /// [DocumentListenOptions] or [QueryListenOptions]) you will receive another
+  /// If you called [DocumentReference.snapshots] or [Query.snapshots] with
+  /// `includeMetadataChanges` parameter set to `true` you will receive another
   /// snapshot with `isFomCache` equal to `false` once the client has received
   /// up-to-date data from the backend.
   final bool isFromCache;