Remove observer properly in ArcPolicyBridge dtor

Previous implementation missed a case where ARC on Demand is active but
OnConnectClosed is never reached.

TEST=Manual testing on DUT
BUG=1424573

Change-Id: I1530c59e4066551037b987d0994e69008b2fd062
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4360679
Auto-Submit: Bryan Yu <yuholong@google.com>
Reviewed-by: Yao Li <yaohuali@google.com>
Commit-Queue: Yao Li <yaohuali@google.com>
Cr-Commit-Position: refs/heads/main@{#1121455}

chrome/browser/ash/arc/policy/arc_policy_bridge.cc

@@ -510,6 +510,11 @@ ArcPolicyBridge::ArcPolicyBridge(content::BrowserContext* context,
 
 ArcPolicyBridge::~ArcPolicyBridge() {
   VLOG(2) << "ArcPolicyBridge::~ArcPolicyBridge";
+  if (is_policy_service_observed) {
+    policy_service_->RemoveObserver(policy::POLICY_DOMAIN_CHROME, this);
+    is_policy_service_observed = false;
+    policy_service_ = nullptr;
+  }
   arc::ArcSessionManager* arc_session_manager = arc::ArcSessionManager::Get();
   // It can be null in unittests
   if (arc_session_manager) {