[CCA] Fix mode selector size not participate relayout bug.

The bug introduced by crrev/c/1778453 remove the mode selector default at
app startup while the UI relayout will reference its width to place the
preview. Fixed by making it invisible but still participating the layout.

Bug: b/141149902
Test: Start CCA, see if the preview is placed correctly.
Change-Id: I99b853133e7cb43f2856a768a8023c64f11fb51a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1807647Reviewed-by: Shik Chen <shik@chromium.org>
Commit-Queue: Shik Chen <shik@chromium.org>
Commit-Queue: Kuo Jen Wei <inker@chromium.org>
Auto-Submit: Kuo Jen Wei <inker@chromium.org>
Cr-Commit-Position: refs/heads/master@{#697119}

chrome/browser/resources/chromeos/camera/src/css/main.css

@@ -261,7 +261,7 @@ div.mode-item>span {
 
 #modes-group.hide,
 .mode-item.hide {
-  display: none;
+  visibility: hidden;
 }
 
 .mode-item>input {