Redundant decorations are applied when navigating to the same code view multiple times

Created by: lguychard

• Sourcegraph version: 18.12.3.2119
• Platform information: Browser extension

Preconditions:

• Activate a Sourcegraph extension that adds decoration when viewing code (eg. Git extras)

Steps to reproduce:

1. Navigate to a code view on github.com
2. Navigate back
3. Navigate forward to the code view again

Expected behavior:

Decorations are displayed only once

Actual behavior:

Decorations are displayed twice. Further navigations to the same code view will keep adding redundant decorations.