Add support to mime types in Files app UI.

ui/file_manager/integration_tests/gallery/open_image_files.js

Index: ui/file_manager/integration_tests/gallery/open_image_files.js
diff --git a/ui/file_manager/integration_tests/gallery/open_image_files.js b/ui/file_manager/integration_tests/gallery/open_image_files.js
index 86fe2464a99b269cb9b2febf71fabb3c9e46a25f..b999a1e6f1c5a8c4eb758a1037f9cef038141f18 100644
--- a/ui/file_manager/integration_tests/gallery/open_image_files.js
+++ b/ui/file_manager/integration_tests/gallery/open_image_files.js
@@ -67,7 +67,7 @@ function openSingleImage(testVolumeName, volumeType) {
  * @return {Promise} Promise to be fulfilled with on success.
  */
 function openMultipleImages(testVolumeName, volumeType) {
-  var testEntries = [ENTRIES.desktop, ENTRIES.image2, ENTRIES.image3];
+  var testEntries = [ENTRIES.desktop, ENTRIES.image3];
   var launchedPromise = launch(testVolumeName, volumeType, testEntries);
   return launchedPromise.then(function(args) {
     var appId = args.appId;
@@ -79,8 +79,8 @@ function openMultipleImages(testVolumeName, volumeType) {
           appId,
           ['.mosaic-tile']
       ).then(function(tiles) {
-        if (tiles.length !== 3)
-          return pending('The number of tiles is expected 3, but is %d',
+        if (tiles.length !== 2)
+          return pending('The number of tiles is expected 2, but is %d',
                          tiles.length);
         return tiles;
       });