Update CSS to delay change in visibility so it matches the overlay

chrome/browser/resources/print_preview/previewarea/preview_area.css

Index: chrome/browser/resources/print_preview/previewarea/preview_area.css
diff --git a/chrome/browser/resources/print_preview/previewarea/preview_area.css b/chrome/browser/resources/print_preview/previewarea/preview_area.css
index 70795297650dc22ffa815d5006558688b18cfe02..78725eefdd5f77e0fa6ebf6057c240fa760671b7 100644
--- a/chrome/browser/resources/print_preview/previewarea/preview_area.css
+++ b/chrome/browser/resources/print_preview/previewarea/preview_area.css
@@ -80,5 +80,12 @@
 }
 
 .preview-area-overlayed {
+  /**
+   * The 100 ms delay here is intended to match that of
+   * #preview-area .preview-area-overlay-layer.invisible
+   * This is important because without this delay there will be a noticeable
+   * flicker whenever the overlay is displayed for a short period of time.
+   */
+  transition: visibility 100ms linear 100ms;

[Dan Beam, 2014/11/04 19:15:13]

i'm amazed visibility is interpolated.
https://developer.mozilla.org/en-US/docs/Web/CSS/visibility#Interpolation

lgtm as long as this is cancelled when new previews finish loading/rendering.

   visibility: hidden;
 }