Cleanup/modernize history_deletion_dialog

- Remove unnecessary indentation
- Use "show-on-attach" attribute instead of custom code
- s/Tap/Click/

Inspired by comments on crrev.com/c/2288850

Bug: none
Change-Id: If0bc7fb58e2d0a41fa272cf90feb014ad859d739
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2309430Reviewed-by: dpapad <dpapad@chromium.org>
Commit-Queue: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#790408}

chrome/browser/resources/settings/clear_browsing_data_dialog/history_deletion_dialog.html

-    <style include="settings-shared"></style>
+<style include="settings-shared"></style>
 
-    <cr-dialog id="dialog" close-text="$i18n{close}">
-      <div slot="title">$i18n{historyDeletionDialogTitle}</div>
-      <div slot="body">$i18nRaw{historyDeletionDialogBody}</div>
-      <div slot="button-container">
-        <cr-button class="action-button" on-click="onOkTap_">
-          $i18n{historyDeletionDialogOK}
-        </cr-button>
-      </div>
-    </cr-dialog>
+<cr-dialog id="dialog" close-text="$i18n{close}" show-on-attach>
+  <div slot="title">$i18n{historyDeletionDialogTitle}</div>
+  <div slot="body">$i18nRaw{historyDeletionDialogBody}</div>
+  <div slot="button-container">
+    <cr-button class="action-button" on-click="onOkClick_">
+      $i18n{historyDeletionDialogOK}
+    </cr-button>
+  </div>
+</cr-dialog>

chrome/browser/resources/settings/clear_browsing_data_dialog/history_deletion_dialog.js

@@ -19,16 +19,11 @@ Polymer({
 
   _template: html`{__html_template__}`,
 
-  /** @override */
-  attached() {
-    this.$.dialog.showModal();
-  },
-
   /**
-   * Tap handler for the "OK" button.
+   * Click handler for the "OK" button.
    * @private
    */
-  onOkTap_() {
+  onOkClick_() {
     this.$.dialog.close();
   },
 });