Sync with CrOS error codes.

Add to ErrorCode and metrics::DownloadErrorCode:

- kInternalLibCurlError
- kUnresolvedHostError
- kUnresolvedHostRecovered

Test: builds
Change-Id: Ibe11c02137860aed583b00b7e05b089ef84edb03
diff --git a/common/error_code_utils.cc b/common/error_code_utils.cc
index b0bbbd4..5bcbaa4 100644
--- a/common/error_code_utils.cc
+++ b/common/error_code_utils.cc
@@ -161,6 +161,12 @@
       return "ErrorCode::kFirstActiveOmahaPingSentPersistenceError";
     case ErrorCode::kVerityCalculationError:
       return "ErrorCode::kVerityCalculationError";
+    case ErrorCode::kInternalLibCurlError:
+      return "ErrorCode::kInternalLibCurlError";
+    case ErrorCode::kUnresolvedHostError:
+      return "ErrorCode::kUnresolvedHostError";
+    case ErrorCode::kUnresolvedHostRecovered:
+      return "ErrorCode::kUnresolvedHostRecovered";
       // Don't add a default case to let the compiler warn about newly added
       // error codes which should be added here.
   }