message: grpc-json transcoder: add integration test
diff: @@ -5,6 +5,7 @@ package bookstore;
  import "google/api/annotations.proto";
  import "google/api/httpbody.proto";
  import "google/protobuf/empty.proto";
  +import "google/protobuf/struct.proto";
  // A simple Bookstore API.
  //
  @@ -90,6 +91,12 @@ service Bookstore {
  get: "/index"
  };
  }
  + rpc EchoStruct(EchoStructReqResp) returns (EchoStructReqResp) {
  + option (google.api.http) = {
  + post: "/echoStruct"
  + body: "content"
  + };
  + }
  }
  // A shelf resource.
  @@ -193,3 +200,9 @@ message GetAuthorRequest {
  // The ID of the author resource to retrieve.
  int64 author = 1;
  }
  +
  +// Request and Response message for EchoStructReqResp method.
  +message EchoStructReqResp {
  + // The content of request.
  + google.protobuf.Struct content = 1;
  +}
  