Gallery: restore the window first if it's minimzed.

If we call show method when window is minimzed, the window flashes. To
prevent it, restore the window first before we show the window.

BUG=563322
TEST=manually tested as described in the issue.

Review URL: https://codereview.chromium.org/1494493002

Cr-Commit-Position: refs/heads/master@{#362656}

ui/file_manager/gallery/js/background.js

@@ -63,7 +63,12 @@ function openGalleryWindow(urls) {
       });
     });
   }).then(function(gallery) {
+    // If the window is minimized, we need to restore it first.
+    if (gallery.rawAppWindow.isMinimized())
+      gallery.rawAppWindow.restore();
+
     gallery.rawAppWindow.show();
+
     return gallery.rawAppWindow.contentWindow.appID;
   }).catch(function(error) {
     console.error('Launch failed' + error.stack || error);