Add field trial testing config for OOP Storage

This adds a config entry for the experimental group in the first stage
of the out-of-process Storage Service rollout.

Bug: 1057802
Change-Id: I2d638fd881d0b8a39d80202278cafdd56eccbfaa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2106756Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Ken Rockot <rockot@google.com>
Cr-Commit-Position: refs/heads/master@{#750835}

testing/variations/fieldtrial_testing_config.json

@@ -5269,6 +5269,27 @@
             ]
         }
     ],
+    "StorageServiceOutOfProcess": [
+        {
+            "platforms": [
+                "chromeos",
+                "linux",
+                "mac",
+                "windows"
+            ],
+            "experiments": [
+                {
+                    "name": "Unsandboxed_BeforeSandboxAvailable",
+                    "enable_features": [
+                        "StorageServiceOutOfProcess"
+                    ],
+                    "disable_features": [
+                        "StorageServiceSandbox"
+                    ]
+                }
+            ]
+        }
+    ],
     "SubresourceRedirect": [
         {
             "platforms": [