src/vs/workbench/services/workingCopy/common/workingCopyHistoryService.ts/WorkingCopyHistoryService/addEntry
class WorkingCopyHistoryService:	async addEntry({ resource, source, timestamp }: IWorkingCopyHistoryEntryDescriptor, token: CancellationToken): Promise<IWorkingCopyHistoryEntry | undefined> {
		if (!this.fileService.hasProvider(resource)) {
			return undefined; // we require the working copy resource to be file service accessible
		}

		// Resolve history model for working copy
		const model = await this.getModel(resource);
		if (token.isCancellationRequested) {
			return undefined;
		}

		// Add to model
		return model.addEntry(source, timestamp, token);
	}