Add param update for ChromeOSNeuralPalm.

Bug: 1009290
Change-Id: I55866a8d591153bc1ef978b924cdb93a03c68f2f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2033057
Auto-Submit: Rob Schonberger <robsc@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Commit-Queue: Alexei Svitkine <asvitkine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#737810}

testing/variations/fieldtrial_testing_config.json

@@ -1486,6 +1486,9 @@
             "experiments": [
                 {
                     "name": "Enabled",
+                    "params": {
+                        "neural_palm_radius_polynomial": "0.17889799, 4.22584412"
+                    },
                     "enable_features": [
                         "EnableNeuralPalmDetectionFilter",
                         "EnableNeuralStylusReportFilter"