[blink scheduler] Allow intensive wake up throttling of pages with WebSocket in testing config.

This CL updates the IntensiveWakeUpThrottling testing config to reflect
the configuration that that we intend to experiment with on M87 Beta.

Since WebSocket event handlers are never throttled, we intend to
remove the WebSocket aggressive throttling opt-out at the same time
as we enable IntensiveWakeUpThrottling.

Bug: 1121725, 1075553
Change-Id: I90b9e6c0ab5da7988f0d5e14ebdfcdc0e4678fd2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2468504
Commit-Queue: Brian White <bcwhite@chromium.org>
Auto-Submit: François Doray <fdoray@chromium.org>
Reviewed-by: Brian White <bcwhite@chromium.org>
Cr-Commit-Position: refs/heads/master@{#817090}

testing/variations/fieldtrial_testing_config.json

@@ -3702,6 +3702,7 @@
                 {
                     "name": "Enabled",
                     "enable_features": [
+                        "AllowAggressiveThrottlingWithWebSocket",
                         "IntensiveWakeUpThrottling"
                     ]
                 }