add configurable min documents to create indexes

Author: cherylEnkidu

firebase-firestore/src/test/java/com/google/firebase/firestore/local/CountingQueryEngine.java

@@ -102,6 +102,11 @@ public void setRelativeIndexReadCostPerDocument(double newCost) {
     queryEngine.setRelativeIndexReadCostPerDocument(newCost);
   }
 
+  @Override
+  public void setMinCollectionSizeToAutoCreateIndex(int newMin) {
+    queryEngine.setMinCollectionSizeToAutoCreateIndex(newMin);
+  }
+
   /**
    * Returns the number of documents returned by the RemoteDocumentCache's `getAll()` API (since the
    * last call to `resetCounts()`)

firebase-firestore/src/test/java/com/google/firebase/firestore/local/LocalStoreTestCase.java

@@ -234,6 +234,10 @@ protected void setRelativeIndexReadCostPerDocument(double newCost) {
     queryEngine.setRelativeIndexReadCostPerDocument(newCost);
   }
 
+  protected void setMinCollectionSizeToAutoCreateIndex(int newMin) {
+    queryEngine.setMinCollectionSizeToAutoCreateIndex(newMin);
+  }
+
   private void releaseTarget(int targetId) {
     localStore.releaseTarget(targetId);
   }