fake attestation flow used in browser test

This CL replaces the complex object construction of AttestationFlow with
FakeAttestationFlow because the consumers of fake attestation flow
doesn't care about the details.

The CL was validated by browser_tests.

BUG=b:158955123

Change-Id: Ida31a3c933ecac639fe86ff9ba62e610e26d2a29
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2297063Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Reviewed-by: Maksim Ivanov <emaxx@chromium.org>
Commit-Queue: Leo Lai <cylai@google.com>
Cr-Commit-Position: refs/heads/master@{#789821}

chrome/browser/chromeos/login/test/local_policy_test_server_mixin.cc

@@ -12,9 +12,7 @@
 #include "chrome/browser/chromeos/login/test/fake_gaia_mixin.h"
 #include "chrome/browser/chromeos/policy/browser_policy_connector_chromeos.h"
 #include "chrome/browser/chromeos/policy/device_cloud_policy_initializer.h"
-#include "chromeos/attestation/mock_attestation_flow.h"
-#include "chromeos/cryptohome/async_method_caller.h"
-#include "chromeos/dbus/cryptohome/fake_cryptohome_client.h"
+#include "chromeos/attestation/fake_attestation_flow.h"
 #include "chromeos/system/fake_statistics_provider.h"
 #include "components/policy/core/common/cloud/cloud_policy_constants.h"
 #include "components/policy/core/common/cloud/policy_builder.h"
@@ -161,10 +159,7 @@ void LocalPolicyTestServerMixin::SetFakeAttestationFlow() {
       ->browser_policy_connector_chromeos()
       ->GetDeviceCloudPolicyInitializer()
       ->SetAttestationFlowForTesting(
-          std::make_unique<chromeos::attestation::AttestationFlow>(
-              cryptohome::AsyncMethodCaller::GetInstance(),
-              chromeos::FakeCryptohomeClient::Get(),
-              std::make_unique<chromeos::attestation::FakeServerProxy>()));
+          std::make_unique<chromeos::attestation::FakeAttestationFlow>());
 }
 
 bool LocalPolicyTestServerMixin::SetDeviceStateRetrievalResponse(