Remove unused include in sequenced_worker_pool.h

storage/browser/blob/blob_data_handle.h

Index: storage/browser/blob/blob_data_handle.h
diff --git a/storage/browser/blob/blob_data_handle.h b/storage/browser/blob/blob_data_handle.h
index 3f4529346b103cc0149d0a507494011e867153dc..4fea47d1039aede37814299a9f7d2a82779a968a 100644
--- a/storage/browser/blob/blob_data_handle.h
+++ b/storage/browser/blob/blob_data_handle.h
@@ -47,6 +47,9 @@ class STORAGE_EXPORT BlobDataHandle
   BlobDataHandle(const BlobDataHandle& other);  // May be copied on any thread.
   ~BlobDataHandle() override;                   // May be deleted on any thread.
 
+  // Assignment operator matching copy constructor.
+  BlobDataHandle& operator=(const BlobDataHandle& other);
+
   // Returns if this blob is still constructing. If so, one can use the
   // RunOnConstructionComplete to wait.
   // Must be called on IO thread.