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/update_manager/chromeos_policy.cc b/update_manager/chromeos_policy.cc
index e3d99d0..9abb21f 100644
--- a/update_manager/chromeos_policy.cc
+++ b/update_manager/chromeos_policy.cc
@@ -129,6 +129,7 @@
     case ErrorCode::kUpdateCanceledByChannelChange:
     case ErrorCode::kOmahaRequestXMLHasEntityDecl:
     case ErrorCode::kFilesystemVerifierError:
+    case ErrorCode::kUserCanceled:
       LOG(INFO) << "Not changing URL index or failure count due to error "
                 << chromeos_update_engine::utils::CodeToString(err_code)
                 << " (" << static_cast<int>(err_code) << ")";
@@ -137,7 +138,7 @@
     case ErrorCode::kSuccess:                            // success code
     case ErrorCode::kUmaReportedMax:                     // not an error code
     case ErrorCode::kOmahaRequestHTTPResponseBase:       // aggregated already
-    case ErrorCode::kDevModeFlag:                       // not an error code
+    case ErrorCode::kDevModeFlag:                        // not an error code
     case ErrorCode::kResumedFlag:                        // not an error code
     case ErrorCode::kTestImageFlag:                      // not an error code
     case ErrorCode::kTestOmahaUrlFlag:                   // not an error code