webservd: Update libchrome APIs to r405848

The new libchrome has been ported from Chromium and some APIs have
changed. Make necessary changes at call sites.

Notable changes from libchrome:
- base::ListValue::iterator now exposes std::unique_ptr<base::Value>
  instead of raw base::Value*.

Bug: 29104761
Change-Id: I01a79fec3329bc0155a8f119e25854b094082aec
1 file changed