Added incident report for variations seed signature mismatch.

chrome/browser/metrics/variations/variations_seed_store.h

Index: chrome/browser/metrics/variations/variations_seed_store.h
diff --git a/chrome/browser/metrics/variations/variations_seed_store.h b/chrome/browser/metrics/variations/variations_seed_store.h
index c81b15e3e0967def607055df822dd13cd7ed7371..cd13c685522335c3aea627f2e53bb65cba5ada34 100644
--- a/chrome/browser/metrics/variations/variations_seed_store.h
+++ b/chrome/browser/metrics/variations/variations_seed_store.h
@@ -55,6 +55,10 @@ class VariationsSeedStore {
   // Registers Local State prefs used by this class.
   static void RegisterPrefs(PrefRegistrySimple* registry);
 
+  // Returns the invalid signature in base64 format, or an empty string if the
+  // signature was not invalid.

[grt (UTC plus 2), 2014/10/15 15:08:07]

shouldn't this be: "..., or an empty string if the signature was valid, missing,
or if signature verification is disabled."? same q for the comment in
variations_service.h. what do you think, alexei?

[Alexei Svitkine (slow), 2014/10/15 15:16:30]

Yeah, that sounds even better!

[Georges Khalil, 2014/10/15 16:53:19]

Done.

+  std::string GetInvalidSignature() const;
+
  protected:
   // Note: UMA histogram enum - don't re-order or remove entries.
   enum VerifySignatureResult {
@@ -88,6 +92,9 @@ class VariationsSeedStore {
   // Cached serial number from the most recently fetched variations seed.
   std::string variations_serial_number_;
 
+  // Keeps track of an invalid signature.
+  std::string invalid_base64_signature_;
+
   DISALLOW_COPY_AND_ASSIGN(VariationsSeedStore);
 };