Add finch field trial for Optimization Hints Fetching.

Bug: 932707
Change-Id: If73900c292289d4646af04a9ff6801d2d52d8049
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1795982Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Auto-Submit: Michael Crouse <mcrouse@chromium.org>
Commit-Queue: Robert Kaplow <rkaplow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#695314}

testing/variations/fieldtrial_testing_config.json

@@ -3966,6 +3966,25 @@
             ]
         }
     ],
+    "OptimizationHintsFetching": [
+        {
+            "platforms": [
+                "android"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled_20190804",
+                    "params": {
+                        "min_top_host_engagement_score_threshold": "3.0",
+                        "top_host_blacklist_size_multiplier": "2.0"
+                    },
+                    "enable_features": [
+                        "OptimizationHintsFetching"
+                    ]
+                }
+            ]
+        }
+    ],
     "OutOfBlinkCors": [
         {
             "platforms": [