platform2: Fix issues with new version of libchrome

libchrome r334380 has the following breaking changes that need to be fixed:
- base::JSONWriter::Write() and base::JSONWriter::WriteWithOptions() take
  "const base::Value&" instead of "const base::Value*"
- base::JSONReader::Read() and base::JSONReader::ReadAndReturnError()
  return a scoped_ptr<base::Value> instead of base::Value*
- base/safe_strerror_posix.h is moved to base/posix/safe_strerror.h
- safe_strerror() is now in "base" namespace
- StartsWithASCII(), EndsWith(), StringToUpperASCII(), LowerCaseEqualsASCII()
  are now in "base" namespace
- ObserverList<T> is now in "base" namespace
- base::PrintTo(base::FilePath) used in gtest is now moved to libchrome-test
  library and as such, unit test runners need to link to this library now.
- crypto::RSAPrivateKey::CreateSensitive() is now removed from //crypto, so
  some of tests in chromeos-login that used that function had to be changed
  to use crypto::GenerateRSAKeyPairNSS() directly.
- UnixDomanSocket class is now in "base" namespace
- Pickle class is now in "base" namespace

BUG=chromium:496469
TEST=`./build_packages`
CQ-DEPEND=CL:277662

Change-Id: I36e5fbf2e36a92068873ffbd44020c862a3ed9e3
Reviewed-on: https://chromium-review.googlesource.com/277671
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>
Trybot-Ready: Alex Vakulenko <avakulenko@chromium.org>
Tested-by: Alex Vakulenko <avakulenko@chromium.org>
diff --git a/buffet/buffet_client.cc b/buffet/buffet_client.cc
index ab8f189..8c9e075 100644
--- a/buffet/buffet_client.cc
+++ b/buffet/buffet_client.cc
@@ -337,8 +337,10 @@
                        ManagerProxy* manager_proxy) {
     ErrorPtr error;
     std::string error_message;
-    std::unique_ptr<base::Value> json(base::JSONReader::ReadAndReturnError(
-        value, base::JSON_PARSE_RFC, nullptr, &error_message));
+    std::unique_ptr<base::Value> json(
+        base::JSONReader::ReadAndReturnError(value, base::JSON_PARSE_RFC,
+                                             nullptr, &error_message)
+            .release());
     if (!json) {
       Error::AddTo(&error, FROM_HERE, chromeos::errors::json::kDomain,
                    chromeos::errors::json::kParseError, error_message);