fieldtrial_testing_config for DiscardCodeCacheAfterFirstUse

We intend to make a wider rollout/experiment of the feature to discard
the code cache. No changes are expected in the lab. Update the config to
confirm no effect on bots.

Bug: 1045052
Change-Id: I5c0a6443f9cefac93391d957a1fcefffc72adea3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2356709Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: Egor Pasko <pasko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#798280}

testing/variations/fieldtrial_testing_config.json

@@ -2353,6 +2353,24 @@
             ]
         }
     ],
+    "DiscardCodeCacheAfterFirstUse": [
+        {
+            "platforms": [
+                "android",
+                "linux",
+                "mac",
+                "windows"
+            ],
+            "experiments": [
+                {
+                    "name": "EnableDiscardCodeCacheAfterFirstUse",
+                    "enable_features": [
+                        "DiscardCodeCacheAfterFirstUse"
+                    ]
+                }
+            ]
+        }
+    ],
     "DnsHttpssvc": [
         {
             "platforms": [