Expose clearPersistence() publicly (#455)

Author: Brian Chen

firebase-firestore/CHANGELOG.md

@@ -2,6 +2,10 @@
 - [fixed] Updated gRPC to 1.21.0. A bug in the prior version would occasionally
   cause a crash if a network state change occurred concurrently with an RPC.
   (#428)
+- [feature] Added `clearPersistence()`, which clears the persistent storage
+  including pending writes and cached documents. This is intended to help
+  write reliable tests (https://github.com/firebase/firebase-js-sdk/issues/449).
+
 
 # 19.0.1
 - [fixed] Fixed an issue that prevented schema migrations for clients with

firebase-firestore/src/main/java/com/google/firebase/firestore/FirebaseFirestore.java

@@ -405,7 +405,8 @@ public static void setLoggingEnabled(boolean loggingEnabled) {
    * @return A Task that is resolved once the persistent storage has been cleared. Otherwise, the
    *     Task is rejected with an error.
    */
-  Task<Void> clearPersistence() {
+  @PublicApi
+  public Task<Void> clearPersistence() {
     final TaskCompletionSource<Void> source = new TaskCompletionSource<>();
     asyncQueue.enqueueAndForget(
         () -> {