Fix thread safety issues in LocalRawGcsService and MemoryBlobStorage.

PiperOrigin-RevId: 899182135
Change-Id: If52fbcc88bf10b029f33eb5f4e2fcd814114c53d

Author: gae-java-bot

api_dev/src/main/java/com/google/appengine/api/blobstore/dev/MemoryBlobStorage.java

@@ -23,8 +23,8 @@
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
-import java.util.HashMap;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 
 /**
  * A version of {@link BlobStorage} that stores all data in memory.
@@ -35,7 +35,7 @@ class MemoryBlobStorage implements BlobStorage {
   private final BlobInfoStorage blobInfoStorage;
 
   MemoryBlobStorage(BlobInfoStorage blobInfoStorage) {
-    this.blobContents = new HashMap<BlobKey, byte[]>();
+    this.blobContents = new ConcurrentHashMap<>();
     this.blobInfoStorage = blobInfoStorage;
   }