Check the enrollment in /home/chronos/Local State in addition to the VPD.

This will allow us to migrate the remaining CfMs to the -cfm flavors of
their board images.

BUG=b:157901191
TEST=unit tests, compared behavior with fizz on a Teemo with and without
requisition in VPD, with and without enrollment in Local State JSON.

Cq-Depend: chromium:2239007
Change-Id: I99b05b8530265d4ef4c81472d0be6ba251f7049c
Reviewed-on: https://chromium-review.googlesource.com/c/aosp/platform/system/update_engine/+/2242361
Tested-by: Matthew Ziegelbaum <ziegs@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
Commit-Queue: Matthew Ziegelbaum <ziegs@chromium.org>
diff --git a/requisition_util.cc b/requisition_util.cc
new file mode 100644
index 0000000..5445bce
--- /dev/null
+++ b/requisition_util.cc
@@ -0,0 +1,69 @@
+//
+// Copyright (C) 2020 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+#include "update_engine/requisition_util.h"
+
+#include <memory>
+#include <vector>
+
+#include <base/files/file_util.h>
+#include <base/json/json_file_value_serializer.h>
+#include <base/logging.h>
+#include <base/strings/string_util.h>
+
+#include "update_engine/common/subprocess.h"
+#include "update_engine/common/utils.h"
+
+using std::string;
+using std::vector;
+
+namespace {
+
+constexpr char kOemRequisitionKey[] = "oem_device_requisition";
+
+}  // namespace
+
+namespace chromeos_update_engine {
+
+string ReadDeviceRequisition(const base::FilePath& local_state) {
+  string requisition;
+  bool vpd_retval = utils::GetVpdValue(kOemRequisitionKey, &requisition);
+
+  // Some users manually convert non-CfM hardware at enrollment time, so VPD
+  // value may be missing. So check the Local State JSON as well.
+  if ((requisition.empty() || !vpd_retval) && base::PathExists(local_state)) {
+    int error_code;
+    std::string error_msg;
+    JSONFileValueDeserializer deserializer(local_state);
+    std::unique_ptr<base::Value> root =
+        deserializer.Deserialize(&error_code, &error_msg);
+    if (!root) {
+      if (error_code != 0) {
+        LOG(ERROR) << "Unable to deserialize Local State with exit code: "
+                   << error_code << " and error: " << error_msg;
+      }
+      return "";
+    }
+    auto* path = root->FindPath({"enrollment", "device_requisition"});
+    if (!path || !path->is_string()) {
+      return "";
+    }
+    path->GetAsString(&requisition);
+  }
+  return requisition;
+}
+
+}  // namespace chromeos_update_engine