[Fuchsia] Ensure to Tear down |agent_services_| before |agent_impl_|.

Change-Id: Ie68765ef6dcf9293f40d901ec9a066d0a530bb9b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1868934
Commit-Queue: Xinan Cheng <xinan@google.com>
Auto-Submit: Xinan Cheng <xinan@google.com>
Reviewed-by: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#707527}

fuchsia/base/fake_component_context.cc

@@ -11,6 +11,7 @@
 #include <utility>
 
 #include "base/logging.h"
+#include "base/run_loop.h"
 
 namespace cr_fuchsia {
 
@@ -45,6 +46,9 @@ void FakeComponentContext::NotImplemented_(const std::string& name) {
   NOTIMPLEMENTED() << " API: " << name;
 }
 
-FakeComponentContext::~FakeComponentContext() = default;
+FakeComponentContext::~FakeComponentContext() {
+  agent_services_.Unbind();
+  base::RunLoop().RunUntilIdle();
+}
 
 }  // namespace cr_fuchsia