redux: Scaffolding for custom replace/revive logic.

Be sure to use our SerializeEscaped wrapper, introduced earlier in
this series, for proper escaping of the '__serializedType__' key, to
prevent a security hole.

This code looks almost exactly the same as it would without our
wrapper.

One key difference is that we use the constant
SERIALIZED_TYPE_FIELD_NAME, exposed by our wrapper and used in its
implementation, to be certain that we're using the same field name
that gets escaped. Fortunately, this is very easy to do.

(If we had used a different string, then, as long as that string
were consistent between our custom replacer and reviver functions,
(1) things would basically work, with no obvious indications that
anything was wrong, and (2) the security hole would reopen.)

src/boot/store.js

@@ -1,6 +1,7 @@
 /* @flow strict-local */
 import { applyMiddleware, compose, createStore } from 'redux';
 import type { Store } from 'redux';
+import Immutable from 'immutable';
 import { persistStore, autoRehydrate } from '../third/redux-persist';
 import type { Config } from '../third/redux-persist';
 
@@ -9,6 +10,9 @@ import rootReducer from './reducers';
 import middleware from './middleware';
 import ZulipAsyncStorage from './ZulipAsyncStorage';
 import createMigration from '../redux-persist-migrate/index';
+import * as SerializeEscaped from './SerializeEscaped';
+
+const { SERIALIZED_TYPE_FIELD_NAME } = SerializeEscaped;
 
 // AsyncStorage.clear(); // use to reset storage during development
 
@@ -143,10 +147,34 @@ const migrations: { [string]: (GlobalState) => GlobalState } = {
   }),
 };
 
+const customReplacer = (key, value, defaultReplacer) =>
+  // Scaffolding for the next commit, where we replace/revive ZulipVersion
+  defaultReplacer(key, value);
+const customReviver = (key, value, defaultReviver) => {
+  if (value !== null && typeof value === 'object' && SERIALIZED_TYPE_FIELD_NAME in value) {
+    // Scaffolding for the next commit, where we replace/revive ZulipVersion
+    const data = value.data; // eslint-disable-line no-unused-vars
+    switch (value[SERIALIZED_TYPE_FIELD_NAME]) {
+      default:
+      // Fall back to defaultReviver, below
+    }
+  }
+  return defaultReviver(key, value);
+};
+
+const { stringify, parse } = SerializeEscaped.immutable(
+  Immutable,
+  null,
+  customReplacer,
+  customReviver,
+);
+
 const reduxPersistConfig: Config = {
   whitelist: [...storeKeys, ...cacheKeys],
   // $FlowFixMe: https://github.com/rt2zz/redux-persist/issues/823
   storage: ZulipAsyncStorage,
+  serialize: stringify,
+  deserialize: parse,
 };
 
 const store: Store<GlobalState, Action> = createStore(