Delete VerdictCacheManager on shutdown

If we don't remove the VerdictCacheManager on Shutdown, it attempts to
access the HostContentSettingsMap after it's been destroyed, leading to
a crash.

Bug: 978412
Change-Id: I88329185de8e3b70f353d781680b564e633e0d5f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1676445Reviewed-by: Varun Khaneja <vakh@chromium.org>
Commit-Queue: Daniel Rubery <drubery@chromium.org>
Cr-Commit-Position: refs/heads/master@{#672261}

chrome/browser/safe_browsing/services_delegate_desktop.cc

@@ -116,6 +116,9 @@ void ServicesDelegateDesktop::ShutdownServices() {
   resource_request_detector_.reset();
   incident_service_.reset();
 
+  // Delete the VerdictCacheManager instances
+  cache_manager_map_.clear();
+
   // Delete the ChromePasswordProtectionService instances.
   password_protection_service_map_.clear();