[finch][code cache] Fix experiment groups for CodeCacheDeduplicationStudy

- Fix experiment groups.

Change-Id: If572af8fe4f60699c8013f75af58328be5c8013f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2576952Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Auto-Submit: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#834974}

testing/variations/fieldtrial_testing_config.json

@@ -1764,7 +1764,10 @@
             ],
             "experiments": [
                 {
-                    "name": "Enabled",
+                    "name": "Enabled_16K",
+                    "params": {
+                        "size": "16384"
+                    },
                     "enable_features": [
                         "CodeCacheDeduplicationStudy"
                     ]