RC: Document the fact that using WS doesn't prevent freezing/discarding

The fact that the LIVE_STATE_USING_WEB_SOCKETS reason exists might
confuse some devs who could assume that using a WebSocket will protect
their page, this add a comment to specify that this heuristic isn't
currently used.

Change-Id: Ibc6034a53c87291993dfa66094b69a2fa55aa0cf
Reviewed-on: https://chromium-review.googlesource.com/c/1319771Reviewed-by: François Doray <fdoray@chromium.org>
Commit-Queue: Sébastien Marchand <sebmarchand@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605750}

chrome/browser/resource_coordinator/decision_details.h

@@ -63,6 +63,7 @@ enum class DecisionFailureReason : int32_t {
   LIVE_STATE_PLAYING_AUDIO,
   // The tab is opted out of the intervention as it is currently using
   // WebSockets.
+  // NOTE: This heuristic isn't used in the freezing/discarding interventions.
   LIVE_STATE_USING_WEB_SOCKETS,
   // The tab is opted out of the intervention as it is currently WebUSB.
   LIVE_STATE_USING_WEB_USB,