Fix default value of mirror settings for external camera

The default value of mirror settings should be set to false only when it
is a user-facing camera. For environment-facing and external cameras,
the default value of mirror settings should be set to true.

Bug: b/140842700
Test: Tested on betty and it works as expectedly.

Change-Id: Ie864b00d8bb5cf48bbc1c33d9acb0922f1ec11ff
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1808622
Commit-Queue: Wei Lee <wtlee@chromium.org>
Reviewed-by: Shik Chen <shik@chromium.org>
Cr-Commit-Position: refs/heads/master@{#697166}

chrome/browser/resources/chromeos/camera/src/js/views/camera/options.js

@@ -224,7 +224,7 @@ cca.views.camera.Options.prototype.updateVideoDeviceId_ = function(
 cca.views.camera.Options.prototype.updateMirroring_ = function(facingMode) {
   // Update mirroring by detected facing-mode. Enable mirroring by default if
   // facing-mode isn't available.
-  var enabled = facingMode ? facingMode == 'user' : true;
+  var enabled = facingMode ? facingMode != 'environment' : true;
 
   // Override mirroring only if mirroring was toggled manually.
   if (this.videoDeviceId_ in this.mirroringToggles_) {