Convert remaining StringToLowerASCII to ToLowerASCII

sync/internal_api/public/base/attachment_id_proto.cc

Index: sync/internal_api/public/base/attachment_id_proto.cc
diff --git a/sync/internal_api/public/base/attachment_id_proto.cc b/sync/internal_api/public/base/attachment_id_proto.cc
index 6692ab70dc77d5bc0411a2222028b85e215ebcf2..b457fc6fad9e763385369529c1ebabc8ef42735a 100644
--- a/sync/internal_api/public/base/attachment_id_proto.cc
+++ b/sync/internal_api/public/base/attachment_id_proto.cc
@@ -13,7 +13,7 @@ namespace syncer {
 sync_pb::AttachmentIdProto CreateAttachmentIdProto(size_t size,
                                                    uint32_t crc32c) {
   sync_pb::AttachmentIdProto proto;
-  std::string guid = base::StringToLowerASCII(base::GenerateGUID());
+  std::string guid = base::ToLowerASCII(base::GenerateGUID());
   DCHECK(!guid.empty());
   // Requirements are that this id must be a unique RFC4122 UUID, formatted in
   // lower case.