src/vs/workbench/api/common/extHostSCM.ts/ExtHostSCM/$provideOriginalResource
class ExtHostSCM:	$provideOriginalResource(sourceControlHandle: number, uriComponents: UriComponents, token: CancellationToken): Promise<UriComponents | null> {
		const uri = URI.revive(uriComponents);
		this.logService.trace('ExtHostSCM#$provideOriginalResource', sourceControlHandle, uri.toString());

		const sourceControl = this._sourceControls.get(sourceControlHandle);

		if (!sourceControl || !sourceControl.quickDiffProvider || !sourceControl.quickDiffProvider.provideOriginalResource) {
			return Promise.resolve(null);
		}

		return asPromise(() => sourceControl.quickDiffProvider!.provideOriginalResource!(uri, token))
			.then<UriComponents | null>(r => r || null);
	}