Add UNSPECIFIED to UserConsent::ConsentStatus enum

It is best practice to have UNSPECIFIED as first value in an enum for
consistent behavior between proto2 and proto3.
No one is sending these events yet, so changing the proto should
be fine.

Bug: 781765
Change-Id: I0b045b8654462f694620144a3f83817043c0e914
Reviewed-on: https://chromium-review.googlesource.com/848973
Reviewed-by: Sky Malice <skym@chromium.org>
Reviewed-by: Martin Šrámek <msramek@chromium.org>
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Commit-Queue: Christian Dullweber <dullweber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#526941}

components/consent_auditor/consent_auditor.cc

@@ -36,7 +36,7 @@ UserEventSpecifics::UserConsent::ConsentStatus ToProtoEnum(
       return UserEventSpecifics::UserConsent::GIVEN;
   }
   NOTREACHED();
-  return UserEventSpecifics::UserConsent::GIVEN;
+  return UserEventSpecifics::UserConsent::UNSPECIFIED;
 }
 
 }  // namespace

components/sync/protocol/proto_enum_conversions.cc

@@ -319,8 +319,9 @@ const char* ProtoEnumToString(
 const char* ProtoEnumToString(
     sync_pb::UserEventSpecifics::UserConsent::ConsentStatus status) {
   ASSERT_ENUM_BOUNDS(sync_pb::UserEventSpecifics::UserConsent, ConsentStatus,
-                     REVOKED, GIVEN);
+                     UNSPECIFIED, GIVEN);
   switch (status) {
+    ENUM_CASE(sync_pb::UserEventSpecifics::UserConsent, UNSPECIFIED);
     ENUM_CASE(sync_pb::UserEventSpecifics::UserConsent, REVOKED);
     ENUM_CASE(sync_pb::UserEventSpecifics::UserConsent, GIVEN);
   }

components/sync/protocol/user_event_specifics.proto

@@ -99,8 +99,9 @@ message UserEventSpecifics {
     optional string locale = 4;
     // Was the consent for |feature| given or revoked?
     enum ConsentStatus {
-      REVOKED = 0;
-      GIVEN = 1;
+      UNSPECIFIED = 0;
+      REVOKED = 1;
+      GIVEN = 2;
     }
     optional ConsentStatus status = 5;
   }