WebXR: Add camera-access-barebones.html to proposal page.

Change-Id: I365392ad1496169e721f2cb2320aea25048c2024
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2356189Reviewed-by: Piotr Bialecki <bialpio@chromium.org>
Commit-Queue: Luis Garcia <luisggarcia@google.com>
Cr-Commit-Position: refs/heads/master@{#798152}

third_party/webxr_test_pages/webxr-samples/proposals/index.html

@@ -126,6 +126,10 @@
             { title: 'AR Lighting estimation', category: 'Phone AR',
               path: 'lighting-estimation.html',
               description: 'Demonstrates using the Lighting Estimation feature.' },
+            { title: 'AR Camera Access', category: 'Phone AR',
+              path: 'camera-access-barebones.html',
+              description: 'Demonstrates using the Camera Access feature to obtain and use a camera ' +
+                           'image texture.' },
           ];
 
           let mainElement = document.getElementById("main");