Migrate usage of deprecated base::Value methods.

Methods provided by base::Value that consume or produce unmanaged raw
pointers have been deprecated and will be eventually removed from
libchrome. This CL migrates the usage of these deprecated methods in the
libweave code to the equivalent methods that use std::unique_ptr.

BUG=chromium:689697
TEST=Run unit tests.

Change-Id: I8cc5bb5d7a6ea742ad46e071db0887430bde5641
Reviewed-on: https://weave-review.googlesource.com/8458
Reviewed-by: Eric Caruso <ejcaruso@google.com>
16 files changed