fido: fix a nonsensical cast in fido_request_handler_unittest

In crrev.com/c/1256016, we moved FidoAuthenticator instantiation and
ownership into the respective FidoDiscovery subclasses. This also
eliminated FidoRequestHandlerBase::CreateAuthenticatorFromDevice() which
was where we previously wrapped a discovered FidoDevice in a
FidoDeviceAuthenticator before adding it to the request handler.

In fido_request_handler_unittest, this was used as a testing seam to
inject a FakeFidoAuthenticator implementation. Injection of the fake was
dropped, but the "real" FidoDeviceAuthenticator was still casted into a
pointer to the fake elsewhere. While this seems to not bother compilers
too much, it's probably a Bad Idea. This CL therefore entirely removes
the FakeFidoAuthenticator class (without changing semantics of the
fixture or the tests).

Bug: 903294
Change-Id: I7a6bad330b1152dc455ded5b6db3d3309f4eb3be
Reviewed-on: https://chromium-review.googlesource.com/c/1340903Reviewed-by: Jun Choi <hongjunchoi@chromium.org>
Commit-Queue: Jun Choi <hongjunchoi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609536}

device/fido/fido_device_authenticator.h

@@ -48,6 +48,7 @@ class COMPONENT_EXPORT(DEVICE_FIDO) FidoDeviceAuthenticator
   base::WeakPtr<FidoAuthenticator> GetWeakPtr() override;
 
   FidoDevice* device() { return device_.get(); }
+  void SetTaskForTesting(std::unique_ptr<FidoTask> task);
 
  protected:
   void OnCtapMakeCredentialResponseReceived(
@@ -57,8 +58,6 @@ class COMPONENT_EXPORT(DEVICE_FIDO) FidoDeviceAuthenticator
       GetAssertionCallback callback,
       base::Optional<std::vector<uint8_t>> response_data);
 
-  void SetTaskForTesting(std::unique_ptr<FidoTask> task);
-
  private:
   void InitializeAuthenticatorDone(base::OnceClosure callback);
 

device/fido/fido_request_handler_unittest.cc

@@ -157,17 +157,6 @@ class FakeFidoTask : public FidoTask {
   base::WeakPtrFactory<FakeFidoTask> weak_factory_;
 };
 
-class FakeFidoAuthenticator : public FidoDeviceAuthenticator {
- public:
-  explicit FakeFidoAuthenticator(std::unique_ptr<FidoDevice> device)
-      : FidoDeviceAuthenticator(std::move(device)) {}
-
-  void RunFakeTask(FakeTaskCallback callback) {
-    SetTaskForTesting(
-        std::make_unique<FakeFidoTask>(device(), std::move(callback)));
-  }
-};
-
 class FakeFidoRequestHandler : public FidoRequestHandler<std::vector<uint8_t>> {
  public:
   FakeFidoRequestHandler(service_manager::Connector* connector,
@@ -185,10 +174,18 @@ class FakeFidoRequestHandler : public FidoRequestHandler<std::vector<uint8_t>> {
   ~FakeFidoRequestHandler() override = default;
 
   void DispatchRequest(FidoAuthenticator* authenticator) override {
-    static_cast<FakeFidoAuthenticator*>(authenticator)
-        ->RunFakeTask(
-            base::BindOnce(&FakeFidoRequestHandler::OnAuthenticatorResponse,
-                           weak_factory_.GetWeakPtr(), authenticator));
+    // FidoRequestHandlerTest uses ScopedFakeDiscovery to inject mock devices
+    // that get wrapped in a FidoDeviceAuthenticator, so we can safely cast
+    // here.
+    auto* device_authenticator =
+        static_cast<FidoDeviceAuthenticator*>(authenticator);
+    // Instead of sending a real CTAP request, send an empty byte array. Note
+    // that during discovery, the device already has received a GetInfo command
+    // at this point.
+    device_authenticator->SetTaskForTesting(std::make_unique<FakeFidoTask>(
+        device_authenticator->device(),
+        base::BindOnce(&FakeFidoRequestHandler::OnAuthenticatorResponse,
+                       weak_factory_.GetWeakPtr(), authenticator)));
   }
 
  private:
@@ -507,7 +504,7 @@ TEST_F(FidoRequestHandlerTest, TestSetPlatformAuthenticator) {
                                       CreateFakeSuccessDeviceResponse());
   device->SetDeviceTransport(FidoTransportProtocol::kInternal);
   auto authenticator =
-      std::make_unique<FakeFidoAuthenticator>(std::move(device));
+      std::make_unique<FidoDeviceAuthenticator>(std::move(device));
 
   TestTransportAvailabilityObserver observer;
   auto request_handler = std::make_unique<FakeFidoRequestHandler>(
@@ -543,7 +540,7 @@ TEST_F(FidoRequestHandlerTest,
                                       CreateFakeSuccessDeviceResponse());
   device->SetDeviceTransport(FidoTransportProtocol::kInternal);
   auto authenticator =
-      std::make_unique<FakeFidoAuthenticator>(std::move(device));
+      std::make_unique<FidoDeviceAuthenticator>(std::move(device));
 
   TestTransportAvailabilityObserver observer;
   auto request_handler = std::make_unique<FakeFidoRequestHandler>(