[Sync] Add size and crc32c to AttachmentId.

sync/internal_api/public/base/attachment_id_proto.h

Index: sync/internal_api/public/base/attachment_id_proto.h
diff --git a/sync/internal_api/public/base/attachment_id_proto.h b/sync/internal_api/public/base/attachment_id_proto.h
index a47f46e2e43c1c211021401e27b527d41438fffd..9af3a9866b4ded7f2cd249df713749a8c5591191 100644
--- a/sync/internal_api/public/base/attachment_id_proto.h
+++ b/sync/internal_api/public/base/attachment_id_proto.h
@@ -5,6 +5,7 @@
 #ifndef SYNC_INTERNAL_API_PUBLIC_BASE_ATTACHMENT_ID_PROTO_H_
 #define SYNC_INTERNAL_API_PUBLIC_BASE_ATTACHMENT_ID_PROTO_H_
 
+#include "base/basictypes.h"
 #include "sync/base/sync_export.h"
 #include "sync/protocol/sync.pb.h"
 
@@ -13,7 +14,13 @@ namespace syncer {
 // Helper functions that are logically part of sync_pb::AttachmentIdProto.
 
 // Creates a unique AttachmentIdProto.
-SYNC_EXPORT_PRIVATE sync_pb::AttachmentIdProto CreateAttachmentIdProto();
+//
+// |size| is the size in bytes of the attachment identified by this proto.
+//
+// |crc32c| is the crc32c of the attachment identified by this proto.
+SYNC_EXPORT_PRIVATE sync_pb::AttachmentIdProto CreateAttachmentIdProto(
+    size_t size,
+    uint32_t crc32c);
 
 // Creates an AttachmentMetadata object from a repeated field of
 // AttachmentIdProto objects.