src/vs/workbench/services/workingCopy/common/workingCopyBackupTracker.ts/WorkingCopyBackupTracker/onDidChangeContent
class WorkingCopyBackupTracker:	private onDidChangeContent(workingCopy: IWorkingCopy): void {

		// Increment content version ID
		const contentVersionId = this.getContentVersion(workingCopy);
		this.mapWorkingCopyToContentVersion.set(workingCopy, contentVersionId + 1);

		// Schedule backup if dirty
		if (workingCopy.isDirty()) {
			// this listener will make sure that the backup is
			// pushed out for as long as the user is still changing
			// the content of the working copy.
			this.scheduleBackup(workingCopy);
		}
	}