Add ErrorCode::kUserCanceled.

To accomodate the posibility of canceling an ongoing update, this patch
adds a new ErrorCode signaling a user canceling the update.

This patch also removes the now useless unittests that checks if you
added a new error code since the compiler fails if you don't add the
error code to the method mentioned in the test.

Bug: None
TEST=FEATURES=test emerge-link update_engine
TEST=`mmma system/update_engine` on edison-eng and aosp_arm-eng

Change-Id: I991dab1dd8b6c0bb0c24d51cca4e1b75440a86b4
diff --git a/metrics_utils.cc b/metrics_utils.cc
index eb99c7d..11260fc 100644
--- a/metrics_utils.cc
+++ b/metrics_utils.cc
@@ -85,6 +85,9 @@
     case ErrorCode::kPostinstallFirmwareRONotUpdatable:
       return metrics::AttemptResult::kPostInstallFailed;
 
+    case ErrorCode::kUserCanceled:
+      return metrics::AttemptResult::kUpdateCanceled;
+
     // We should never get these errors in the update-attempt stage so
     // return internal error if this happens.
     case ErrorCode::kError:
@@ -201,6 +204,7 @@
     case ErrorCode::kUnsupportedMinorPayloadVersion:
     case ErrorCode::kOmahaRequestXMLHasEntityDecl:
     case ErrorCode::kFilesystemVerifierError:
+    case ErrorCode::kUserCanceled:
       break;
 
     // Special flags. These can't happen (we mask them out above) but