[Payments] Basic validation in the credit card editor.

chrome/browser/ui/views/payments/validating_textfield.cc

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/browser/ui/views/payments/validating_textfield.h"
+
+#include "base/strings/utf_string_conversions.h"
+
+namespace payments {
+
+ValidatingTextfield::ValidatingTextfield(
+    ValidatingTextfield::Delegate* delegate)
+    : Textfield(), delegate_(delegate) {}
+
+void ValidatingTextfield::OnBlur() {
+  Textfield::OnBlur();
+
+  // The first validation of non-empty data should be on a blur. The subsequent
+  // validations will occur when the contents changes.
+  if (!was_validated_ && !text().empty()) {
+    was_validated_ = true;
+    Validate();
+  }
+}
+
+void ValidatingTextfield::OnContentsChanged() {
+  // Validation on every keystroke only happens if the field has been validated
+  // before as part of a blur.
+  if (!was_validated_)
+    return;
+
+  Validate();
+}
+
+void ValidatingTextfield::Validate() {
+  // ValidateTextfield may have side-effects, such as displaying errors.
+  SetInvalid(!delegate_->ValidateTextfield(this));
+}
+
+}  // namespace payments