Remove the persistence checkbox from external protocol handler UI.

We realized in a conversation around issue 951540 that we don't have settings UI
that allows users to reconsider decisions they've made around external protocol
support. Until we work that out, and make longer-term decisions about the
permission model around the feature generally, we should stop making the problem
worse by removing that checkbox from the UI.

Based on existing telemetry (`BrowserDialogs.ExternalProtocol.HandleState`),
this will affect ~8% of users who interact with the dialog, which itself is a
fairly small group of Chrome's users overall.

Bug: 982341, 987149
Change-Id: I723979aab9606d1c2337a36a8f5a0686b95bb9be
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1708070
Commit-Queue: Mike West <mkwst@chromium.org>
Reviewed-by: Kamila Hasanbega <hkamila@google.com>
Reviewed-by: Bret Sepulveda <bsep@chromium.org>
Reviewed-by: Emily Stark <estark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#680353}

chrome/browser/ui/views/external_protocol_dialog.cc

@@ -42,7 +42,9 @@ void ExternalProtocolHandler::RunExternalProtocolDialog(
   new ExternalProtocolDialog(std::move(delegate), web_contents);
 }
 
-ExternalProtocolDialog::~ExternalProtocolDialog() {}
+ExternalProtocolDialog::~ExternalProtocolDialog() {
+  delete remember_decision_checkbox_;
+}
 
 gfx::Size ExternalProtocolDialog::CalculatePreferredSize() const {
   constexpr int kDialogContentWidth = 400;
@@ -108,7 +110,11 @@ ExternalProtocolDialog::ExternalProtocolDialog(
   DCHECK(delegate_->GetMessageText().empty());
   remember_decision_checkbox_ =
       new views::Checkbox(delegate_->GetCheckboxText());
-  AddChildView(remember_decision_checkbox_);
+  remember_decision_checkbox_->SetChecked(false);
+
+  // TODO(982341): We intentionally don't add |remember_decision_checkbox_| to
+  // the dialog, as we're reevaluating whether we actually want persistence
+  // for this mechanism going forward.
 
   constrained_window::ShowWebModalDialogViews(this, web_contents);
   chrome::RecordDialogCreation(chrome::DialogIdentifier::EXTERNAL_PROTOCOL);