Add OomIntervention config to fieldtrial_testing_config

This CL adds a parameter to fieldtrial_testing_config to test a new feature of Oomintervention in
 finch now that canary/dev results look good.

Bug: 879026,764481
Change-Id: I44f0c472db191ce92404a714ef33304992e251b4
Reviewed-on: https://chromium-review.googlesource.com/1183043
Commit-Queue: Yuzu Saijo <yuzus@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589427}

testing/variations/fieldtrial_testing_config.json

@@ -2916,9 +2916,11 @@
             ],
             "experiments": [
                 {
-                    "name": "Intervention_R3",
+                    "name": "Intervention_R7",
                     "params": {
-                        "pause_renderer": "true"
+                        "navigate_ads": "true",
+                        "pause_renderer": "true",
+                        "renderer_workload_threshold_percentage": "16"
                     },
                     "enable_features": [
                         "OomIntervention"