Update fieldtrial_testing_config.json to add an experiment for PageLoadMetricsTimerDelay

Bug: 847269
Change-Id: Iaaf308b473a2f20db769f72ca421a99fe658cb36
Reviewed-on: https://chromium-review.googlesource.com/1079203
Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Reviewed-by: Bryan McQuade <bmcquade@chromium.org>
Commit-Queue: Luna Lu <loonybear@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#563243}(cherry picked from commit 638c712)
Reviewed-on: https://chromium-review.googlesource.com/1079736
Reviewed-by: Luna Lu <loonybear@chromium.org>
Cr-Commit-Position: refs/branch-heads/3440@{#61}
Cr-Branched-From: 010ddcf-refs/heads/master@{#561733}

Author: loonybear

testing/variations/fieldtrial_testing_config.json

@@ -2416,6 +2416,28 @@
             ]
         }
     ],
+    "PageLoadMetricsTimerDelay": [
+        {
+            "platforms": [
+                "android",
+                "chromeos",
+                "linux",
+                "mac",
+                "win"
+            ],
+            "experiments": [
+                {
+                    "name": "10MS",
+                    "params": {
+                        "BufferTimerDelayMillis": "10"
+                    },
+                    "enable_features": [
+                        "PageLoadMetricsTimerDelay"
+                    ]
+                }
+            ]
+        }
+    ],
     "ParallelDownloading": [
         {
             "platforms": [