Distinguish between SCT invalidity reasons in UMA

net/cert/sct_status_flags.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_CERT_SCT_STATUS_FLAGS_H_
 #define NET_CERT_SCT_STATUS_FLAGS_H_
 
 namespace net {
 
 namespace ct {
 
 // The possible verification statuses for a SignedCertificateTimestamp.
 // Note: The numeric values are used within histograms and should not change
 // or be re-assigned.
 enum SCTVerifyStatus {
   // Not a real status, this just prevents a default int value from being
   // mis-interpreseted as a valid status.
   // Also used to count SCTs that cannot be decoded in the histogram.
   SCT_STATUS_NONE = 0,
 
   // The SCT is from an unknown log, so we cannot verify its signature.
   SCT_STATUS_LOG_UNKNOWN = 1,
 
-  // The SCT is from a known log, but the signature is invalid.
-  SCT_STATUS_INVALID = 2,
+  // SCTVerifyStatus=2 used to represent SCT_STATUS_INVALID, which has now been
+  // split into INVALID_SIGNATURE and INVALID_TIMESTAMP to represent the
+  // different reasons an SCT could be invalid.
 
   // The SCT is from a known log, and the signature is valid.
   SCT_STATUS_OK = 3,
 
-  // Used to bound the enum values.
-  SCT_STATUS_MAX,
+  // The SCT is from a known log, but the signature is invalid.
+  SCT_STATUS_INVALID_SIGNATURE = 4,
+
+  // The SCT is from a known log, but the timestamp is in the future.
+  SCT_STATUS_INVALID_TIMESTAMP = 5,
+
+  // Used to bound the enum values. Since this enum is passed over IPC,
+  // the last value must be a valid one (rather than one past a valid one).
+  SCT_STATUS_MAX = SCT_STATUS_INVALID_TIMESTAMP,
 };
 
 }  // namespace ct
 
 }  // namespace net
 
 #endif  // NET_CERT_SCT_STATUS_FLAGS_H_