Reland "Add PermissionChip feature to fieldtrial_testing_config.json."

This is a reland of 39053ccc. The failing
test that caused this to be reverted was deleted in crrev.com/c/2550812.
There are no changes to this CL.

Original change's description:
> Add PermissionChip feature to fieldtrial_testing_config.json.
>
> As a prerequisite to landing cr/339683181.
>
> Bug: 1134294
> Change-Id: I95a0774957c5ba1cae28faad5916865f50e5a8d7
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2510054
> Commit-Queue: Bret Sepulveda <bsep@chromium.org>
> Reviewed-by: Brian White <bcwhite@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#829185}

TBR=bcwhite@chromium.org

Bug: 1134294
Change-Id: I16c604b1a46a924d497fc62424a7edcb2d4653fd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2566994Reviewed-by: Bret Sepulveda <bsep@chromium.org>
Commit-Queue: Bret Sepulveda <bsep@chromium.org>
Cr-Commit-Position: refs/heads/master@{#832340}

testing/variations/fieldtrial_testing_config.json

@@ -5392,6 +5392,24 @@
             ]
         }
     ],
+    "PermissionChip": [
+        {
+            "platforms": [
+                "chromeos",
+                "linux",
+                "mac",
+                "windows"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "PermissionChip"
+                    ]
+                }
+            ]
+        }
+    ],
     "PermissionPromptUICocoa": [
         {
             "platforms": [