Set initial default download path

fix #9822

Auditors: @bridiver, @bbondy, @bsclifton

Test Plan:
a. Manual Test
1. Open Brave with fresh profile
2. Go to about:preferences#general
3. It should show default download path instead of empty

b. unit test

app/browser/reducers/downloadsReducer.js

@@ -14,17 +14,25 @@ const {cancelDownload, pauseDownload, resumeDownload} = require('../electronDown
 const {CANCEL, PAUSE, RESUME} = require('../../common/constants/electronDownloadItemActions')
 const appActions = require('../../../js/actions/appActions')
 const userPrefs = require('../../../js/state/userPrefs')
+const getSetting = require('../../../js/settings').getSetting
 
 const downloadsReducer = (state, action) => {
   const download = action.downloadId ? state.getIn(['downloads', action.downloadId]) : undefined
   if (!download &&
       ![appConstants.APP_MERGE_DOWNLOAD_DETAIL,
         appConstants.APP_CLEAR_COMPLETED_DOWNLOADS,
         appConstants.APP_SELECT_DEFAULT_DOWNLOAD_PATH,
-        appConstants.APP_CHANGE_SETTING].includes(action.actionType)) {
+        appConstants.APP_CHANGE_SETTING,
+        appConstants.APP_SET_STATE].includes(action.actionType)) {
     return state
   }
   switch (action.actionType) {
+    case appConstants.APP_SET_STATE:
+      if (getSetting(settings.DOWNLOAD_DEFAULT_PATH) === '') {
+        const defaultPath = app.getPath('downloads')
+        appActions.changeSetting(settings.DOWNLOAD_DEFAULT_PATH, defaultPath)
+      }
+      break
     case appConstants.APP_DOWNLOAD_REVEALED:
       fs.access(download.get('savePath'), fs.constants.F_OK, (err) => {
         if (err) {

test/unit/app/browser/reducers/downloadsReducerTest.js

@@ -6,10 +6,12 @@ const process = require('process')
 const assert = require('assert')
 const uuid = require('uuid')
 const path = require('path')
+const appActions = require('../../../../../js/actions/appActions')
 const fakeElectron = require('../../../lib/fakeElectron')
 
 const appConstants = require('../../../../../js/constants/appConstants')
 const {PENDING, IN_PROGRESS, RESUMING, PAUSED, COMPLETED, CANCELLED, INTERRUPTED} = require('../../../../../js/constants/downloadStates')
+const settings = require('../../../../../js/constants/settings')
 const {CANCEL} = require('../../../../../app/common/constants/electronDownloadItemActions')
 require('../../../braveUnit')
 
@@ -32,17 +34,35 @@ const oneDownloadWithState = (state) => Immutable.fromJS({
 
 describe('downloadsReducer', function () {
   let downloadsReducer
+  let fakeSettings
+  let downloadDefaultPath
+  let changeSettingSpy
   before(function () {
     mockery.enable({
       warnOnReplace: false,
       warnOnUnregistered: false,
       useCleanCache: true
     })
+
+    fakeSettings = {
+      getSetting: (settingKey, settingsCollection) => {
+        switch (settingKey) {
+          case settings.DOWNLOAD_DEFAULT_PATH:
+            return downloadDefaultPath
+        }
+      }
+    }
+
+    changeSettingSpy = sinon.spy(appActions, 'changeSetting')
+
     mockery.registerMock('electron', fakeElectron)
+    mockery.registerMock('../../../js/settings', fakeSettings)
+    mockery.registerMock('../../../js/actions/appActions', appActions)
     downloadsReducer = require('../../../../../app/browser/reducers/downloadsReducer')
   })
 
   after(function () {
+    changeSettingSpy.restore()
     mockery.disable()
   })
 
@@ -257,4 +277,19 @@ describe('downloadsReducer', function () {
       })
     })
   })
+
+  describe('APP_SET_STATE', function () {
+    it('DOWNLOAD_DEFAULT_PATH is empty', function () {
+      changeSettingSpy.reset()
+      downloadDefaultPath = ''
+      downloadsReducer({}, {actionType: appConstants.APP_SET_STATE})
+      assert(changeSettingSpy.withArgs(settings.DOWNLOAD_DEFAULT_PATH, `${process.cwd()}/downloads`).calledOnce)
+    })
+    it('DOWNLOAD_DEFAULT_PATH is not empty', function () {
+      changeSettingSpy.reset()
+      downloadDefaultPath = '123'
+      downloadsReducer({}, {actionType: appConstants.APP_SET_STATE})
+      assert(changeSettingSpy.notCalled)
+    })
+  })
 })