Expose BlobStoreManager.waitForIdle() as @TestApi.

Bug: 151035961
Test: atest --test-mapping cts/hostsidetests/blobstore
Change-Id: I3632560c5ba9b28b4492d07d847911196b0abc78
diff --git a/apex/blobstore/framework/java/android/app/blob/BlobStoreManager.java b/apex/blobstore/framework/java/android/app/blob/BlobStoreManager.java
index d1e28e9..c759585 100644
--- a/apex/blobstore/framework/java/android/app/blob/BlobStoreManager.java
+++ b/apex/blobstore/framework/java/android/app/blob/BlobStoreManager.java
@@ -22,6 +22,7 @@
 import android.annotation.IntRange;
 import android.annotation.NonNull;
 import android.annotation.SystemService;
+import android.annotation.TestApi;
 import android.content.Context;
 import android.os.ParcelFileDescriptor;
 import android.os.ParcelableException;
@@ -481,6 +482,7 @@
      *
      * @hide
      */
+    @TestApi
     public void waitForIdle(long timeoutMillis) throws InterruptedException, TimeoutException {
         try {
             final CountDownLatch countDownLatch = new CountDownLatch(1);
diff --git a/api/test-current.txt b/api/test-current.txt
index a42710d..88f26bb 100644
--- a/api/test-current.txt
+++ b/api/test-current.txt
@@ -590,6 +590,14 @@
 
 }
 
+package android.app.blob {
+
+  public class BlobStoreManager {
+    method public void waitForIdle(long) throws java.lang.InterruptedException, java.util.concurrent.TimeoutException;
+  }
+
+}
+
 package android.app.prediction {
 
   public final class AppPredictionContext implements android.os.Parcelable {