Add ChangeExtensionEventPageSuspendDelay to testing config.

Preliminary results from the Canary+Dev experiment are encouraging.
Adding to testing config to allow Beta experiments.

Bug: 1144166
Change-Id: Ie40d0c5f46ab2779c2a6ec3c55b21cdfec79abb4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2541004Reviewed-by: Brian White <bcwhite@chromium.org>
Commit-Queue: François Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#828975}

testing/variations/fieldtrial_testing_config.json

@@ -1354,6 +1354,27 @@
             ]
         }
     ],
+    "ChangeExtensionEventPageSuspendDelay": [
+        {
+            "platforms": [
+                "chromeos",
+                "linux",
+                "mac",
+                "windows"
+            ],
+            "experiments": [
+                {
+                    "name": "ChangeExtensionEventPageSuspendDelay",
+                    "params": {
+                        "event-page-suspend-delay-ms": "61000"
+                    },
+                    "enable_features": [
+                        "ChangeExtensionEventPageSuspendDelay"
+                    ]
+                }
+            ]
+        }
+    ],
     "CheckOfflineCapability": [
         {
             "platforms": [