Adds ChangeTabSwitcherPosition to Field Trial Testing Configuration

Bug: 1073826
Change-Id: I378c67f926df54bd4bd75d0a64f7b241534238a7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2208971
Commit-Queue: Ewann Pellé <ewannpv@chromium.org>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#775055}

testing/variations/fieldtrial_testing_config.json

@@ -2871,6 +2871,21 @@
             ]
         }
     ],
+    "IOSChangeTabSwitcherPosition": [
+        {
+            "platforms": [
+                "ios"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "ChangeTabSwitcherPosition"
+                    ]
+                }
+            ]
+        }
+    ],
     "IOSCrashReportBreadcrumbs": [
         {
             "platforms": [