Updating fieldtrial params to match OptimizationHintsFetching experiment.

Change-Id: I04c17fe523a7d2701695c92c3026dfffefa7e95e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1814763
Auto-Submit: Michael Crouse <mcrouse@chromium.org>
Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Commit-Queue: Robert Kaplow <rkaplow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#698493}

testing/variations/fieldtrial_testing_config.json

@@ -4028,8 +4028,8 @@
                 {
                     "name": "Enabled_20190804",
                     "params": {
-                        "min_top_host_engagement_score_threshold": "3.0",
-                        "top_host_blacklist_size_multiplier": "2.0"
+                        "min_top_host_engagement_score_threshold": "2.0",
+                        "top_host_blacklist_size_multiplier": "3.0"
                     },
                     "enable_features": [
                         "OptimizationHintsFetching"