Android: Print the error code string from the client.

The update_engine_client needs to translate the numeric ErrorCode to a
string name that can be printed on the output. This patch moves the
ErrorCodeToString() function to a new error_code_utils.{h,cc} pair of
files so it can be included easily from the client binary and uses it
in the Android update_engine_client.

Bug: 25631767
Bug: 25598547
TEST=`update_engine_client --update` prints the error message in a non-Brillo device.

Change-Id: Ib40813924ec676f3e703412de90d389b2596177e
diff --git a/common/error_code_utils.h b/common/error_code_utils.h
new file mode 100644
index 0000000..ae3958e
--- /dev/null
+++ b/common/error_code_utils.h
@@ -0,0 +1,34 @@
+//
+// Copyright (C) 2012 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.
+//
+
+#ifndef UPDATE_ENGINE_COMMON_ERROR_CODE_UTILS_H_
+#define UPDATE_ENGINE_COMMON_ERROR_CODE_UTILS_H_
+
+#include <string>
+
+#include "update_engine/common/error_code.h"
+
+namespace chromeos_update_engine {
+namespace utils {
+
+// Returns a string representation of the ErrorCodes (either the base
+// error codes or the bit flags) for logging purposes.
+std::string ErrorCodeToString(ErrorCode code);
+
+}  // namespace utils
+}  // namespace chromeos_update_engine
+
+#endif  // UPDATE_ENGINE_COMMON_ERROR_CODE_UTILS_H_