Enable tests related to the extensions web ui that were flaky.

chrome/test/data/webui/print_preview.js

Index: chrome/test/data/webui/print_preview.js
diff --git a/chrome/test/data/webui/print_preview.js b/chrome/test/data/webui/print_preview.js
index 720ecd430baa56ec7bde6d349714c6f7f6af172a..f5b20c0f0155a15904fb58308cdc1f46b22297f9 100644
--- a/chrome/test/data/webui/print_preview.js
+++ b/chrome/test/data/webui/print_preview.js
@@ -187,17 +187,7 @@ PrintPreviewWebUITest.prototype = {
     ];
     this.nativeLayer_ = printPreview.nativeLayer_;
 
-    // Make all transitions and animations take 0ms for testing purposes.
-    // Animations still happen and must be waited on.
-    var noAnimationStyle = document.createElement('style');
-    noAnimationStyle.textContent =
-      '* {' +
-      '  -webkit-transition-duration: 0ms !important;' +
-      '  -webkit-transition-delay: 0ms !important;' +
-      '  -webkit-animation-duration: 0ms !important;' +
-      '  -webkit-animation-delay: 0ms !important;' +
-      '}';
-    document.querySelector('head').appendChild(noAnimationStyle);
+    testing.Test.disableAnimationsAndTransitions();
   }
 };