attestation: Fix policy observer expiry check.

chrome/browser/chromeos/attestation/attestation_policy_observer.h

Index: chrome/browser/chromeos/attestation/attestation_policy_observer.h
diff --git a/chrome/browser/chromeos/attestation/attestation_policy_observer.h b/chrome/browser/chromeos/attestation/attestation_policy_observer.h
index ec595370545e1b652ccfed09318b6358c841f033..a29de51538e369e8ac4c10312628e88c0b8f4637 100644
--- a/chrome/browser/chromeos/attestation/attestation_policy_observer.h
+++ b/chrome/browser/chromeos/attestation/attestation_policy_observer.h
@@ -63,7 +63,9 @@ class AttestationPolicyObserver {
   // Gets the existing EMK certificate and sends it to CheckCertificateExpiry.
   void GetExistingCertificate();
 
-  // Checks if the given certificate is expired and, if so, get a new one.
+  // Checks if the given certificate is expired and, if so, gets a new one. The
+  // certificate data is assumed to actually be a chain of certificates in PEM
+  // format. All certificates in the chain are checked for expiry.
   void CheckCertificateExpiry(const std::string& certificate);

[Mattias Nissler (ping if slow), 2015/12/10 08:08:40]

nit: Please update the variable name to reflect the semantics, i.e.
|pem_certificate_chain| or somesuch.

 
   // Uploads a certificate to the policy server.