Store report cache using buffer

SQLite doesn't detect the binary even if stored in BLOB if the type is not
buffer.

issue2704
review1941002
(transplanted from 3b77f743131cb946fbecd50bc49cb418c67d584e)

--HG--
extra : transplant_source : %3Bw%F7C%13%1C%B9F%FB%EC%D5%0B%C4%9C%B4%18%C6%7DXN