bindings: Fix LargeBlob support in Credentials

Credentials type converter can access a dictionary member[1] when it is
not available.
This CL fixes the issue.


[1] PublicKeyCredentialCreationOptions.extensions.largeBlob.support

Bug: 839389
Change-Id: Ica1b43775e221a37a4be0befc920035f32fa214f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2558133Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Hitoshi Yoshida <peria@chromium.org>
Cr-Commit-Position: refs/heads/master@{#830987}

third_party/blink/renderer/modules/credentialmanager/credential_manager_type_converters.cc

@@ -321,12 +321,15 @@ TypeConverter<AuthenticatorAttachment, base::Optional<String>>::Convert(
 }
 
 // static
-LargeBlobSupport TypeConverter<LargeBlobSupport, String>::Convert(
-    const String& large_blob_support) {
-  if (large_blob_support == "required")
-    return LargeBlobSupport::REQUIRED;
-  if (large_blob_support == "preferred")
-    return LargeBlobSupport::PREFERRED;
+LargeBlobSupport
+TypeConverter<LargeBlobSupport, base::Optional<String>>::Convert(
+    const base::Optional<String>& large_blob_support) {
+  if (large_blob_support) {
+    if (*large_blob_support == "required")
+      return LargeBlobSupport::REQUIRED;
+    if (*large_blob_support == "preferred")
+      return LargeBlobSupport::PREFERRED;
+  }
 
   // Unknown values are treated as preferred.
   return LargeBlobSupport::PREFERRED;
@@ -570,9 +573,12 @@ TypeConverter<PublicKeyCredentialCreationOptionsPtr,
                  WebAuthenticationResidentKeyRequirementEnabled());
       mojo_options->cred_props = true;
     }
-    if (extensions->largeBlob()) {
-      mojo_options->large_blob_enable =
-          ConvertTo<LargeBlobSupport>(extensions->largeBlob()->support());
+    if (extensions->hasLargeBlob()) {
+      base::Optional<WTF::String> support;
+      if (extensions->largeBlob()->hasSupport()) {
+        support = extensions->largeBlob()->support();
+      }
+      mojo_options->large_blob_enable = ConvertTo<LargeBlobSupport>(support);
     }
   }
 

third_party/blink/renderer/modules/credentialmanager/credential_manager_type_converters.h

@@ -106,8 +106,10 @@ struct TypeConverter<blink::mojom::blink::AuthenticatorAttachment,
 };
 
 template <>
-struct TypeConverter<blink::mojom::blink::LargeBlobSupport, String> {
-  static blink::mojom::blink::LargeBlobSupport Convert(const String&);
+struct TypeConverter<blink::mojom::blink::LargeBlobSupport,
+                     base::Optional<String>> {
+  static blink::mojom::blink::LargeBlobSupport Convert(
+      const base::Optional<String>&);
 };
 
 template <>