Adding the Copresence RpcHandler and HttpPost helper.

components/copresence/proto/rpcs.proto

Index: components/copresence/proto/rpcs.proto
diff --git a/components/copresence/proto/rpcs.proto b/components/copresence/proto/rpcs.proto
index bdbed2ec9cb26925fa77f99f2dc3e4da371a5160..22b868ff2abf4ec936d8400a6bf71620d282a0a3 100644
--- a/components/copresence/proto/rpcs.proto
+++ b/components/copresence/proto/rpcs.proto
@@ -5,24 +5,19 @@ import "codes.proto";
 import "enums.proto";
 import "data.proto";
 message RequestHeader {
-  optional DeviceRegistration device_id = 3 [deprecated = true];
   optional ClientVersion client_version = 4;
   optional ClientVersion framework_version = 5;
   optional int64 current_time_millis = 6;
   optional string registered_device_id = 7;
   repeated string experiment_override = 8;
   optional string configuration_etag = 11;
-  extensions 9 to 9;
 }
 message ResponseHeader {
-  optional ErrorType error_type = 1 [deprecated = true];
   optional DebugInfo debug_info = 2;
   optional Status status = 3;
 }
 message RegisterDeviceRequest {
   optional RequestHeader header = 1;
-  optional DeviceRegistration old_registration = 2 [deprecated = true];
-  optional DeviceRegistration new_registration = 3 [deprecated = true];
   optional PushServiceRegistration push_service = 5;
   optional DeviceIdentifiers device_identifiers = 6;
 }
@@ -43,12 +38,10 @@ message UpdateSignalsRequest {
 message ManageMessagesRequest {
   repeated PublishedMessage message_to_publish = 1;
   repeated string id_to_unpublish = 2;
-  optional DeleteAll delete_all = 3;
 }
 message ManageSubscriptionsRequest {
   repeated Subscription subscription = 1;
   repeated string id_to_unsubscribe = 2;
-  optional DeleteAll delete_all = 3;
 }
 message ReportResponse {
   optional ResponseHeader header = 1;
@@ -65,10 +58,8 @@ message UpdateSignalsResponse {
 message ManageMessagesResponse {
   optional util.error.Code status = 1;
   repeated MessageResult published_message_result = 3;
-  extensions 2 to 2;
 }
 message ManageSubscriptionsResponse {
   optional util.error.Code status = 1;
   repeated SubscriptionResult subscription_result = 3;
-  extensions 2 to 2;
 }