webauthn: add test for oversized credential IDs (take two).

Gerrit threw a 500 when uploading the final version of [1] and I didn't
notice. Then the CQ landed the wrong version.

This change includes the final set of code-review replies.

[1] https://chromium-review.googlesource.com/c/chromium/src/+/982634

TBR=engedy

Change-Id: I400c713dedadb2bfac5629994a048a775c0c14b8
Reviewed-on: https://chromium-review.googlesource.com/998184Reviewed-by: Adam Langley <agl@chromium.org>
Reviewed-by: Balazs Engedy <engedy@chromium.org>
Commit-Queue: Adam Langley <agl@chromium.org>
Cr-Commit-Position: refs/heads/master@{#548566}

content/browser/webauth/authenticator_impl_unittest.cc

@@ -656,13 +656,14 @@ TEST_F(AuthenticatorImplTest, TestGetAssertionTimeout) {
 }
 
 TEST_F(AuthenticatorImplTest, OversizedCredentialId) {
-  device::test::ScopedVirtualFidoDevice virtual_device_;
-  TestServiceManagerContext smc_;
+  device::test::ScopedVirtualFidoDevice scoped_virtual_device;
+  TestServiceManagerContext service_manager_context;
+
   // 255 is the maximum size of a U2F credential ID. We also test one greater
   // (256) to ensure that nothing untoward happens.
   const std::vector<size_t> kSizes = {255, 256};
 
-  for (size_t size : kSizes) {
+  for (const size_t size : kSizes) {
     SCOPED_TRACE(size);
 
     SimulateNavigation(GURL(kTestOrigin1));
@@ -675,7 +676,7 @@ TEST_F(AuthenticatorImplTest, OversizedCredentialId) {
 
     const bool should_be_valid = size < 256;
     if (should_be_valid) {
-      ASSERT_TRUE(virtual_device_.mutable_state()->InjectRegistration(
+      ASSERT_TRUE(scoped_virtual_device.mutable_state()->InjectRegistration(
           credential->id, kTestRelyingPartyId));
     }
 

device/fido/virtual_fido_device.h

@@ -69,7 +69,7 @@ class COMPONENT_EXPORT(DEVICE_FIDO) VirtualFidoDevice : public FidoDevice {
     // typically be a domain, e.g. "example.com").
     //
     // Returns true on success. Will fail if there already exists a credential
-    // with the given ID.
+    // with the given ID or if private-key generation fails.
     bool InjectRegistration(const std::vector<uint8_t>& credential_id,
                             const std::string& relying_party_id);