IndexedDB: Test that Blink ack's blobs upon receipt.

storage/browser/blob/blob_storage_context.h

Index: storage/browser/blob/blob_storage_context.h
diff --git a/storage/browser/blob/blob_storage_context.h b/storage/browser/blob/blob_storage_context.h
index 86610cfdfcdbcd31700dcf40b395ee0ef726581d..175e900200e321c8d846b9c37c3424f7c479973e 100644
--- a/storage/browser/blob/blob_storage_context.h
+++ b/storage/browser/blob/blob_storage_context.h
@@ -62,6 +62,7 @@ class STORAGE_EXPORT BlobStorageContext
   void RevokePublicBlobURL(const GURL& url);
 
   size_t memory_usage() const { return memory_usage_; }
+  size_t blob_count() const { return blob_map_.size(); }
 
  private:
   friend class content::BlobStorageHost;