webauthn: don't show a back button in the attestation permission UI sheet

Bug: 961818
Change-Id: I160878b36492ed5adde3a110661bd082df0301c5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1606961
Commit-Queue: Martin Kreichgauer <martinkr@google.com>
Commit-Queue: Adam Langley <agl@chromium.org>
Auto-Submit: Martin Kreichgauer <martinkr@google.com>
Reviewed-by: Adam Langley <agl@chromium.org>
Cr-Commit-Position: refs/heads/master@{#658799}

chrome/browser/ui/webauthn/sheet_models.cc

@@ -1082,6 +1082,10 @@ base::string16 AttestationPermissionRequestSheetModel::GetStepDescription()
       GetRelyingPartyIdString(dialog_model()));
 }
 
+bool AttestationPermissionRequestSheetModel::IsBackButtonVisible() const {
+  return false;
+}
+
 bool AttestationPermissionRequestSheetModel::IsAcceptButtonVisible() const {
   return true;
 }

chrome/browser/ui/webauthn/sheet_models.h

@@ -504,6 +504,7 @@ class AttestationPermissionRequestSheetModel
       ImageColorScheme color_scheme) const override;
   base::string16 GetStepTitle() const override;
   base::string16 GetStepDescription() const override;
+  bool IsBackButtonVisible() const override;
   bool IsAcceptButtonVisible() const override;
   bool IsAcceptButtonEnabled() const override;
   base::string16 GetAcceptButtonLabel() const override;