Print Preview: Add test to verify button order

Add automated test to verify that there are 2 buttons in the print
header and they are in the correct order for all platforms. Split off
parent CL, which contains a fix for the bug linked.

Bug: 880562
Change-Id: I3472561dd1af7e75a86bf4821fb4ae42e82a0d5f
Reviewed-on: https://chromium-review.googlesource.com/1205717Reviewed-by: Scott Chen <scottchen@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#588746}

chrome/test/data/webui/print_preview/header_test.js

@@ -10,6 +10,7 @@ cr.define('header_test', function() {
     HeaderWithCopies: 'header with copies',
     HeaderWithNup: 'header with nup',
     HeaderChangesForState: 'header changes for state',
+    ButtonOrder: 'button order',
   };
 
   const suiteName = 'HeaderTest';
@@ -139,6 +140,27 @@ cr.define('header_test', function() {
       assertEquals(testError, summary.textContent);
       assertTrue(printButton.disabled);
     });
+
+    // Tests that the buttons are in the correct order for different platforms.
+    // See https://crbug.com/880562.
+    test(assert(TestNames.ButtonOrder), function() {
+      // Verify that there are only 2 buttons.
+      assertEquals(2, header.shadowRoot.querySelectorAll('button').length);
+
+      const firstButton = header.$$('button:first-child');
+      const lastButton = header.$$('button:last-child');
+      const printButton = header.$$('button.print');
+      const cancelButton = header.$$('button.cancel');
+
+      if (cr.isWindows || cr.isChromeOS) {
+        // On Windows and Chrome OS, the print button is on the left.
+        assertEquals(firstButton, printButton);
+        assertEquals(lastButton, cancelButton);
+      } else {
+        assertEquals(firstButton, cancelButton);
+        assertEquals(lastButton, printButton);
+      }
+    });
   });
 
   return {

chrome/test/data/webui/print_preview/new_print_preview_ui_browsertest.js

@@ -914,6 +914,10 @@ TEST_F('PrintPreviewHeaderTest', 'HeaderChangesForState', function() {
   this.runMochaTest(header_test.TestNames.HeaderChangesForState);
 });
 
+TEST_F('PrintPreviewHeaderTest', 'ButtonOrder', function() {
+  this.runMochaTest(header_test.TestNames.ButtonOrder);
+});
+
 PrintPreviewDestinationItemTest = class extends NewPrintPreviewTest {
   /** @override */
   get browsePreload() {