Record firstRunTimestamp in sessionStore

Auditors: @bsclifton

Test Plan:

Upgrading existing userData
1. Be on `master` and close Brave
2. Open session-store-1 with less (e.g. ~/Library/Application\ Support/brave-development/session-store-1)
3. See firstRunTimestamp is not there
4. Check out this branch
5. Open Brave, then close it
6. View again session-store-1 and see firstRunTimestamp is there
8. Restart Brave again, then close it
9. See firstRunTimestamp is see firstRunTimestamp is unchanged

New profile
1. Delete userData dir (e.g. ~/Library/Application\ Support/brave-development)
2. Open Brave
3. Close Brave
4. View session-store-1 and see firstRunTimestamp

app/sessionStore.js

@@ -356,6 +356,9 @@ module.exports.loadAppState = () => {
         module.exports.cleanAppData(data, false)
       }
       data = Object.assign(module.exports.defaultAppState(), data)
+      if (!data.firstRunTimestamp) {
+        data.firstRunTimestamp = new Date().getTime()
+      }
       data.cleanedOnShutdown = false
       // Always recalculate the update status
       if (data.updates) {

docs/state.md

@@ -9,6 +9,7 @@ AppStore
 
 ```javascript
 {
+  firstRunTimestamp: integer,
   extensions: {
     [id]: { // the unique id of the extension
       id: string,

test/app/sessionStoreTest.js

@@ -60,4 +60,45 @@ describe('sessionStore', function () {
       yield Brave.app.client.waitForExist(navigatorBookmarked)
     })
   })
+
+  describe('firstRunTimestamp', function () {
+    Brave.beforeAllServerSetup(this)
+    before(function * () {
+      // AY: Why do I need to start, stop and start for this to work properly?
+      yield Brave.startApp()
+      yield setup(Brave.app.client)
+      yield Brave.stopApp(false)
+      yield Brave.startApp()
+      yield setup(Brave.app.client)
+    })
+
+    after(function * () {
+      yield Brave.stopApp()
+    })
+
+    it('sets it once', function * () {
+      const timestamp = new Date().getTime()
+      let firstRunTimestamp
+      yield Brave.app.client
+        .waitUntil(function () {
+          return this.getAppState().then((val) => {
+            firstRunTimestamp = val.value.firstRunTimestamp
+            return (
+              firstRunTimestamp > (timestamp - 30 * 1000) &&
+              firstRunTimestamp <= timestamp
+            )
+          })
+        })
+
+      yield Brave.stopApp(false)
+      yield Brave.startApp()
+      yield setup(Brave.app.client)
+      yield Brave.app.client
+        .waitUntil(function () {
+          return this.getAppState().then((val) => {
+            return (val.value.firstRunTimestamp === firstRunTimestamp)
+          })
+        })
+    })
+  })
 })