Store attachment crc in AttachmentStore

sync/internal_api/public/attachments/attachment_uploader_impl.h

Index: sync/internal_api/public/attachments/attachment_uploader_impl.h
diff --git a/sync/internal_api/public/attachments/attachment_uploader_impl.h b/sync/internal_api/public/attachments/attachment_uploader_impl.h
index fde544c59c1e39da44bfa80b912161b6372ddab3..31944261e4fc2a8d77948666672fd4278529a9ae 100644
--- a/sync/internal_api/public/attachments/attachment_uploader_impl.h
+++ b/sync/internal_api/public/attachments/attachment_uploader_impl.h
@@ -51,14 +51,12 @@ class SYNC_EXPORT AttachmentUploaderImpl : public AttachmentUploader,
   static GURL GetURLForAttachmentId(const GURL& sync_service_url,
                                     const AttachmentId& attachment_id);
 
-  // Return the crc32c of the memory described by |data| and |size|.
+  // Format crc32c to pass into X-Goog-Hash header
   //
   // The value is base64 encoded, big-endian format.  Suitable for use in the
   // X-Goog-Hash header
   // (https://cloud.google.com/storage/docs/reference-headers#xgooghash).
-  //
-  // Potentially expensive.
-  static std::string ComputeCrc32cHash(const char* data, size_t size);
+  static std::string FormatCrc32cHash(uint32_t crc);
 
  private:
   class UploadState;