Fix bug with context menu in Layers3DView.

Review URL: https://codereview.chromium.org/312193002

Review URL: https://codereview.chromium.org/312193002

git-svn-id: svn://svn.chromium.org/blink/trunk@175543 bbb929c8-8fbe-4397-9dbb-9b2b20218538