Avoid UI unresponsiveness when switching between large images.

ui/file_manager/gallery/js/gallery_item.js

Index: ui/file_manager/gallery/js/gallery_item.js
diff --git a/ui/file_manager/gallery/js/gallery_item.js b/ui/file_manager/gallery/js/gallery_item.js
index 53c12eb474c56363269ab51e0ff33d58bf7abd98..685da4fa414323709b41bc3e08ec8960050ff70a 100644
--- a/ui/file_manager/gallery/js/gallery_item.js
+++ b/ui/file_manager/gallery/js/gallery_item.js
@@ -440,3 +440,23 @@ GalleryItem.prototype.rename = function(displayName) {
     this.entry_ = entry;
   }.bind(this));
 };
+
+/**
+ * The threshold size of an image in pixels, which we always use thumbnail
+ * image for slide-in animation above this. This is a hack to avoid an UI
+ * unresponsiveness when switching between images.
+ *
+ * @type{number}
+ */
+GalleryItem.HEAVY_RENDERING_THRESHOLD_PIXELS = 4e3 * 3e3;

[fukino, 2017/01/13 02:50:33]

nit: prefer 4000 * 3000 for easier read.

[yamaguchi, 2017/01/13 12:25:39]

Done.

+
+/**
+ * Whether the image requires long rendering time.
+ *
+ * @return {boolean}
+ */
+GalleryItem.prototype.requireLongRenderingTime = function() {
+  var numPixels = this.metadataItem_.imageHeight *

[oka, 2017/01/13 04:23:19]

I think imageHeight can be undefined. Maybe it's better to early-return if
imageHeight/width is undefined for readability.

[yamaguchi, 2017/01/13 12:25:39]

Done.

+      this.metadataItem_.imageWidth;
+  return numPixels > GalleryItem.HEAVY_RENDERING_THRESHOLD_PIXELS;
+};