Extract temp path util

Summary:
`electron.remote` access is slow so we can cache this
like we do in other places. Also means one fewer `electron`
import which is gonna add up for Flipper Decap.

Reviewed By: mweststrate

Differential Revision: D30247431

fbshipit-source-id: 90f0e8df99af8bed40fbebcfd445abaca2965b7c

desktop/app/src/devices/IOSDevice.tsx

@@ -12,7 +12,6 @@ import child_process, {ChildProcess} from 'child_process';
 import BaseDevice from './BaseDevice';
 import JSONStream from 'JSONStream';
 import {Transform} from 'stream';
-import electron from 'electron';
 import fs from 'fs';
 import {v1 as uuid} from 'uuid';
 import path from 'path';
@@ -21,6 +20,7 @@ import {exec} from 'child_process';
 import {default as promiseTimeout} from '../utils/promiseTimeout';
 import {IOSBridge} from '../utils/IOSBridge';
 import split2 from 'split2';
+import {getAppTempPath} from '../utils/pathUtils';
 
 type IOSLogLevel = 'Default' | 'Info' | 'Debug' | 'Error' | 'Fault';
 
@@ -69,7 +69,7 @@ export default class IOSDevice extends BaseDevice {
       return Buffer.from([]);
     }
     const tmpImageName = uuid() + '.png';
-    const tmpDirectory = (electron.app || electron.remote.app).getPath('temp');
+    const tmpDirectory = getAppTempPath();
     const tmpFilePath = path.join(tmpDirectory, tmpImageName);
     const command =
       this.deviceType === 'emulator'

desktop/app/src/utils/pathUtils.tsx

@@ -9,7 +9,9 @@
 
 import path from 'path';
 import fs from 'fs';
-import {remote} from 'electron';
+// In utils this is fine when used with caching.
+// eslint-disable-next-line flipper/no-electron-remote-imports
+import {default as electron, remote} from 'electron';
 import config from '../fb-stubs/config';
 
 let _staticPath = '';
@@ -55,6 +57,17 @@ export function getAppPath() {
   return _appPath;
 }
 
+let _tempPath: string | undefined = undefined;
+export function getAppTempPath() {
+  if (!_tempPath) {
+    // We cache this.
+    // eslint-disable-next-line no-restricted-properties
+    _tempPath = (electron.app || electron.remote.app).getPath('temp');
+  }
+
+  return _tempPath;
+}
+
 export function getChangelogPath() {
   const changelogPath = getStaticPath(config.isFBBuild ? 'facebook' : '.');
   if (fs.existsSync(changelogPath)) {