CookieStore: Switch CookieChangeSubscription to proto3.

The change makes all proto fields optional, and slightly simplifies the
decoding logic.

CookieChangeSubscription::Serialize() sets all the proto's fields, so
the change is only relevant for corrupt protos. In this case, proto3
will report default values for missing fields.

The change is compatible with previously written data, as proto2 and
proto3 use the same on-disk format.

Bug: 729800
Change-Id: I06b08ce003b571b716bccd540fa15918ea925bb8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2036393Reviewed-by: Ayu Ishii <ayui@chromium.org>
Commit-Queue: Victor Costan <pwnall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#737905}

content/browser/cookie_store/cookie_change_subscription.cc

@@ -40,9 +40,10 @@ network::mojom::CookieMatchType CookieMatchTypeFromProto(
       return network::mojom::CookieMatchType::EQUALS;
     case proto::CookieMatchType::STARTS_WITH:
       return ::network::mojom::CookieMatchType::STARTS_WITH;
+    default:
+      // The on-disk value was corrupted.
+      return network::mojom::CookieMatchType::EQUALS;
   }
-  NOTREACHED();
-  return network::mojom::CookieMatchType::EQUALS;
 }
 
 }  // namespace
@@ -102,16 +103,13 @@ CookieChangeSubscription::ToMojoVector(
 std::unique_ptr<CookieChangeSubscription> CookieChangeSubscription::Create(
     proto::CookieChangeSubscriptionProto proto,
     int64_t service_worker_registration_id) {
-  if (!proto.has_url())
-    return nullptr;
-  GURL url = GURL(proto.url());
+  GURL url(proto.url());
   if (!url.is_valid())
     return nullptr;
 
-  std::string name = proto.has_name() ? proto.name() : "";
+  std::string name = proto.name();
   ::network::mojom::CookieMatchType match_type =
-      proto.has_match_type() ? CookieMatchTypeFromProto(proto.match_type())
-                             : ::network::mojom::CookieMatchType::EQUALS;
+      CookieMatchTypeFromProto(proto.match_type());
 
   return std::make_unique<CookieChangeSubscription>(
       std::move(url), std::move(name), match_type,

content/browser/cookie_store/cookie_change_subscriptions.proto

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-syntax = "proto2";
+syntax = "proto3";
 
 option optimize_for = LITE_RUNTIME;
 
@@ -16,9 +16,9 @@ enum CookieMatchType {
 
 // A single cookie change subscription.
 message CookieChangeSubscriptionProto {
-  required string url = 1;
-  optional string name = 2;
-  optional CookieMatchType match_type = 3;
+  string url = 1;
+  string name = 2;
+  CookieMatchType match_type = 3;
 }
 
 // All cookie change subscriptions belonging to a service worker registration.