Add a new constructor for FileAttachment to support precomputation of mime type and attachment type.

PiperOrigin-RevId: 672643121

sharing/file_attachment.cc

@@ -56,10 +56,11 @@ std::string MimeTypeFromPath(const std::filesystem::path& path) {
 }  // namespace
 
 FileAttachment::FileAttachment(std::filesystem::path file_path,
+                               absl::string_view mime_type,
                                std::string parent_folder, int32_t batch_id,
                                SourceType source_type)
     : Attachment(Attachment::Family::kFile, /*size=*/0, batch_id, source_type),
-      mime_type_(MimeTypeFromPath(file_path)),
+      mime_type_(mime_type.empty() ? MimeTypeFromPath(file_path) : mime_type),
       type_(FileAttachmentTypeFromMimeType(mime_type_)),
       file_path_(std::move(file_path)),
       parent_folder_(std::move(parent_folder)) {

sharing/file_attachment.h

@@ -36,6 +36,7 @@ class FileAttachment : public Attachment {
   using Type = nearby::sharing::service::proto::FileMetadata::Type;
 
   explicit FileAttachment(std::filesystem::path file_path,
+                          absl::string_view mime_type = "",
                           std::string parent_folder = "", int32_t batch_id = 0,
                           SourceType source_type = SourceType::kUnknown);
   FileAttachment(int64_t id, int64_t size, std::string file_name,