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/common/error_code.h b/common/error_code.h
index 2bbdcfa..32155f2 100644
--- a/common/error_code.h
+++ b/common/error_code.h
@@ -71,6 +71,7 @@
   kUnsupportedMinorPayloadVersion = 45,
   kOmahaRequestXMLHasEntityDecl = 46,
   kFilesystemVerifierError = 47,
+  kUserCanceled = 48,
 
   // VERY IMPORTANT! When adding new error codes:
   //
@@ -122,8 +123,8 @@
   // Mask that indicates bit positions that are used to indicate special flags
   // that are embedded in the error code to provide additional context about
   // the system in which the error was encountered.
-  kSpecialFlags = (kDevModeFlag | kResumedFlag | kTestImageFlag |
-                   kTestOmahaUrlFlag)
+  kSpecialFlags =
+      (kDevModeFlag | kResumedFlag | kTestImageFlag | kTestOmahaUrlFlag)
 };
 
 inline std::ostream& operator<<(std::ostream& os, ErrorCode val) {