[SessionStorageS13N] Fixing StoragePartitionImpl RemoveLocalStorage tests

Session was assuming that InitiateConnection() would always complete
asynchronously. In tests, this doesn't happen. This fixes one case where
a callback was registered after the call to InitiateConnection()

Bug: 716490
Change-Id: I606446ba5e5ba5907c9c37ab440cc38bef2838d8
Reviewed-on: https://chromium-review.googlesource.com/1112486Reviewed-by: Marijn Kruisselbrink <mek@chromium.org>
Commit-Queue: Daniel Murphy <dmurph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569742}

content/browser/dom_storage/session_storage_context_mojo.cc

@@ -581,8 +581,9 @@ void SessionStorageContextMojo::RunWhenConnected(base::OnceClosure callback) {
     case NO_CONNECTION:
       // If we don't have a filesystem_connection_, we'll need to establish one.
       connection_state_ = CONNECTION_IN_PROGRESS;
+      on_database_opened_callbacks_.push_back(std::move(callback));
       InitiateConnection();
-      FALLTHROUGH;
+      return;
     case CONNECTION_IN_PROGRESS:
       // Queue this OpenSessionStorage call for when we have a level db pointer.
       on_database_opened_callbacks_.push_back(std::move(callback));