Adds a merge functionality for the COCOEvaluator for distributed workflow.

PiperOrigin-RevId: 621024221

Author: genehwung

Diff for: models/official/detection/evaluation/coco_evaluator.py

@@ -361,6 +361,20 @@ def update(self, predictions, groundtruths=None):
         else:
           self._groundtruths[k].append(v)
 
+  def merge(self, other):
+    """Merges the states from the other CocoEvaluator."""
+    for k, v in other._predictions.items():  # pylint: disable=protected-access
+      if k not in self._predictions:
+        self._predictions[k] = v
+      else:
+        self._predictions[k].extend(v)
+
+    for k, v in other._groundtruths.items():  # pylint: disable=protected-access
+      if k not in self._groundtruths:
+        self._groundtruths[k] = v
+      else:
+        self._groundtruths[k].extend(v)
+
 
 class ShapeMaskCOCOEvaluator(COCOEvaluator):
   """COCO evaluation metric class for ShapeMask."""