CrOs first-run UI polished.

chrome/browser/resources/chromeos/first_run/preload.css

Index: chrome/browser/resources/chromeos/first_run/preload.css
diff --git a/chrome/browser/resources/chromeos/first_run/preload.css b/chrome/browser/resources/chromeos/first_run/preload.css
new file mode 100644
index 0000000000000000000000000000000000000000..b8b3d3bda73b9f81bd766b7d63cb34c08cc4a6b4
--- /dev/null
+++ b/chrome/browser/resources/chromeos/first_run/preload.css
@@ -0,0 +1,53 @@
+/**
+ * Copyright 2013 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.
+ */
+
+/**
+ * Preloads images. Without preloading, background image starts loading in
+ * the moment when CSS property is applied. Image loading has visible delay and
+ * looks like defect.
+ */
+
+@media all and (-webkit-max-device-pixel-ratio: 1.5) {
+  body::after {
+    content:
+        url('chrome://resources/images/apps/button.png')
+        url('chrome://resources/images/apps/button_hover.png')
+        url('chrome://resources/images/apps/button_pressed.png')
+        url('chrome://resources/images/apps/button_focused.png')
+        url('chrome://resources/images/apps/button_focused_hover.png')
+        url('chrome://resources/images/apps/button_focused_pressed.png')
+        url('chrome://resources/images/apps/button_inactive.png')
+        url('chrome://resources/images/apps/blue_button.png')
+        url('chrome://resources/images/apps/blue_button_hover.png')
+        url('chrome://resources/images/apps/blue_button_pressed.png')
+        url('chrome://resources/images/apps/blue_button_focused.png')
+        url('chrome://resources/images/apps/blue_button_focused_hover.png')
+        url('chrome://resources/images/apps/blue_button_focused_pressed.png')
+        url('chrome://resources/images/apps/blue_button_inactive.png');
+    display: none;
+  }
+}
+
+@media all and (-webkit-min-device-pixel-ratio: 1.5) {
+  body::after {
+    content:
+        url('chrome://resources/images/2x/apps/button.png')
+        url('chrome://resources/images/2x/apps/button_hover.png')
+        url('chrome://resources/images/2x/apps/button_pressed.png')
+        url('chrome://resources/images/2x/apps/button_focused.png')
+        url('chrome://resources/images/2x/apps/button_focused_hover.png')
+        url('chrome://resources/images/2x/apps/button_focused_pressed.png')
+        url('chrome://resources/images/2x/apps/button_inactive.png')
+        url('chrome://resources/images/2x/apps/blue_button.png')
+        url('chrome://resources/images/2x/apps/blue_button_hover.png')
+        url('chrome://resources/images/2x/apps/blue_button_pressed.png')
+        url('chrome://resources/images/2x/apps/blue_button_focused.png')
+        url('chrome://resources/images/2x/apps/blue_button_focused_hover.png')
+        url('chrome://resources/images/2x/apps/blue_button_focused_pressed.png')
+        url('chrome://resources/images/2x/apps/blue_button_inactive.png');
+    display: none;
+  }
+}