libweave: change base::Value to enum class type Upstream this is an enum class and the names of the values are slightly different. CQ-DEPEND=CL:907588 BUG=b:37434548 TEST=emerge with unit tests Change-Id: Id37cadb0ff2d70bedb74d1be8102f8c4c5c86f67 Reviewed-on: https://chromium-review.googlesource.com/907318 Tested-by: Eric Caruso <[email protected]> Reviewed-by: Luis Hector Chavez <[email protected]>