Backport observeHandle._fetch from shark

packages/minimongo/observe.js

@@ -175,5 +175,33 @@ LocalCollection._observeFromObserveChanges = function (cursor, observeCallbacks)
     {callbacks: observeChangesCallbacks});
   var handle = cursor.observeChanges(changeObserver.applyChange);
   suppressed = false;
+
+  if (changeObserver.ordered) {
+    // Fetches the current list of documents, in order, as an array.  Can be
+    // called at any time.  Internal API assumed by the `observe-sequence`
+    // package (used by Meteor UI for `#each` blocks).  Only defined on ordered
+    // observes (those that listen on `addedAt` or similar).  Continues to work
+    // after `stop()` is called on the handle.
+    //
+    // Because we already materialize the full OrderedDict of all documents, it
+    // seems nice to provide access to the view rather than making the data
+    // consumer reconstitute it.  This gives the consumer a shot at doing
+    // something smart with the feed like proxying it, since firing callbacks
+    // like `changed` and `movedTo` basically requires omniscience (knowing old
+    // and new documents, old and new indices, and the correct value for
+    // `before`).
+    //
+    // NOTE: If called from an observe callback for a certain change, the result
+    // is *not* guaranteed to be a snapshot of the cursor up to that
+    // change. This is because the callbacks are invoked before updating docs.
+    handle._fetch = function () {
+      var docsArray = [];
+      changeObserver.docs.forEach(function (doc) {
+        docsArray.push(transform(doc));
+      });
+      return docsArray;
+    };
+  }
+
   return handle;
 };