Fix DCHECK in SecurityState::SetProcessLock().

Restoring DCHECK to verify the lock being passed in like it did
before http://crrev.com/c/2246923 . This fixes an accidental behavior
change that wasn't noticed during review.

Bug: 1067389
Change-Id: I4059e5482196e3e5a1120c5ff192922fb89919be
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2298800
Auto-Submit: Aaron Colwell <acolwell@chromium.org>
Commit-Queue: Alex Moshchuk <alexmos@chromium.org>
Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#788690}

content/browser/child_process_security_policy_impl.cc

@@ -483,7 +483,7 @@ class ChildProcessSecurityPolicyImpl::SecurityState {
   void SetProcessLock(const ProcessLock& lock,
                       BrowsingInstanceId browsing_instance_id) {
     DCHECK(process_lock_.is_empty());
-    DCHECK_NE(SiteInstanceImpl::GetDefaultSiteURL(), process_lock_.lock_url());
+    DCHECK_NE(SiteInstanceImpl::GetDefaultSiteURL(), lock.lock_url());
     process_lock_ = lock;
     DCHECK(lowest_browsing_instance_id_.is_null());
     lowest_browsing_instance_id_ = browsing_instance_id;