Fix crash when opening app menu during extension uninstallation

This CL adds a missing null check for
HostedAppBrowserController::GetExtension() when constructing the hosted
app menu.

Bug: 923309
Change-Id: I102a1cf5a845ebb65d2e6eed54e862b45d0c92ce
Reviewed-on: https://chromium-review.googlesource.com/c/1426243
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Commit-Queue: Dominick Ng <dominickn@chromium.org>
Auto-Submit: Alan Cutter <alancutter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#625036}
3 files changed