resetStore doesn't clear the cache if it was populated with cache's .restore method initially and no queries are run on the page

[d-dmytro]

Intended outcome:
I used the client.resetStore() method to clear cache after logging out a user. I populate the cache with the data from the server initially (on page load) using the cache's .restore method, like this:

new ApolloClient({
    connectToDevTools: true,
    ssrMode: false,
    link: createUploadLink({
        uri: `${apiHost}/graphql`,
        credentials: "include",
        headers: { cookie: options.cookie }
    }),
    cache: new InMemoryCache().restore(initialState || {})
});

No queries or mutations happen on the page initially. When the user clicks logout, I expect apollo-client to clear the cache that I populated initially.

Actual outcome:

When the user logs out, the client.resetStore() method does not clear the data that was populated with the InMemoryCache's restore method. The cache is not cleared as the QueryManager is not initialized at the moment I call the resetStore (or the user logs out), it is initialized only when some query or mutation occurs. This is where apollo-client checks whether the QueryManager exists, and if not it skips clearing the cache:
https://github.com/apollographql/apollo-client/blob/master/packages/apollo-client/src/ApolloClient.ts#L402

How to reproduce the issue:
I described how to reproduce the issue in the text above. Basically, you need to init the ApolloClient with cache populated using the .restore() method. The app shouldn't fire any query or mutation on initialization, which causes this.queryManager to not be initialized.

Versions
Binaries:
Node: 8.9.4 - /usr/local/bin/node
Yarn: 1.3.2 - /usr/local/bin/yarn
npm: 5.6.0 - /usr/local/bin/npm
npmPackages:
apollo-cache-inmemory: ^1.2.1 => 1.2.1
apollo-client: ^2.3.1 => 2.3.1
apollo-upload-client: ^8.0.0 => 8.0.0
react-apollo: ^2.1.4 => 2.1.4

[hwillson]

#3885 adds a new client.clearStore() method to the public API, that will clear the store without refetching active queries. Thanks!

[d-dmytro]

Thank you :)