Add a fieldtrial testing config for CacheStorageHighPriorityMatch.

Bug: 1018920
Change-Id: I1f6686557d9ff7bd101549cc09a09fc525341942
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1936851
Commit-Queue: Ben Kelly <wanderview@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#719310}

testing/variations/fieldtrial_testing_config.json

@@ -1468,6 +1468,25 @@
             ]
         }
     ],
+    "CacheStorageHighPriorityMatch": [
+        {
+            "platforms": [
+                "windows",
+                "mac",
+                "chromeos",
+                "linux",
+                "android"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled4",
+                    "enable_features": [
+                        "CacheStorageHighPriorityMatch"
+                    ]
+                }
+            ]
+        }
+    ],
     "CacheStorageSequence": [
         {
             "platforms": [