Fix crash in AssistantManagerServiceImpl::OnStartFinished

The |Service::Context| object is used by |AssistantManagerServiceImpl|
but it was destructed first during teardown, causing a use-after-free
error.

Bug: 1162128
Test: compiled
Change-Id: I44a6a52387879602d67057dafc482a50d482d265
Cq-Include-Trybots: luci.chrome.try:linux-chromeos-chrome
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2605578
Commit-Queue: Tao Wu <wutao@chromium.org>
Auto-Submit: Jeroen Dhollander <jeroendh@chromium.org>
Reviewed-by: Tao Wu <wutao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#839633}

chromeos/services/assistant/service.cc

@@ -216,10 +216,10 @@ class Service::Context : public ServiceContext {
 Service::Service(std::unique_ptr<network::PendingSharedURLLoaderFactory>
                      pending_url_loader_factory,
                  signin::IdentityManager* identity_manager)
-    : identity_manager_(identity_manager),
+    : context_(std::make_unique<Context>(this)),
+      identity_manager_(identity_manager),
       token_refresh_timer_(std::make_unique<base::OneShotTimer>()),
       main_task_runner_(base::SequencedTaskRunnerHandle::Get()),
-      context_(std::make_unique<Context>(this)),
       pending_url_loader_factory_(std::move(pending_url_loader_factory)) {
   DCHECK(identity_manager_);
   chromeos::PowerManagerClient* power_manager_client =

chromeos/services/assistant/service.h

@@ -154,6 +154,12 @@ class COMPONENT_EXPORT(ASSISTANT_SERVICE) Service
   // for the device.
   bool ShouldEnableHotword();
 
+  // |ServiceContext| object passed to child classes so they can access some of
+  // our functionality without depending on us.
+  // Note: this is used by the other members here, so it must be defined first
+  // so it is destroyed last.
+  std::unique_ptr<ServiceContext> context_;
+
   signin::IdentityManager* const identity_manager_;
   std::unique_ptr<ScopedAshSessionObserver> scoped_ash_session_observer_;
   ScopedObserver<ash::AmbientUiModel, ash::AmbientUiModelObserver>
@@ -183,10 +189,6 @@ class COMPONENT_EXPORT(ASSISTANT_SERVICE) Service
 
   base::Optional<std::string> access_token_;
 
-  // |ServiceContext| object passed to child classes so they can access some of
-  // our functionality without depending on us.
-  std::unique_ptr<ServiceContext> context_;
-
   // non-null until |assistant_manager_service_| is created.
   std::unique_ptr<network::PendingSharedURLLoaderFactory>
       pending_url_loader_factory_;