Enable AudioServiceSandbox flag in audio service field trial testing on Windows and Mac.

This reverts commit 9a13eecb.

Reason for revert: Enable sandbox only for Windows and Mac. Leave sandbox disabled on Linux until I fix #890850.

Original change's description:
> Revert "Enable AudioServiceSandbox flag in audio service field trial testing."
>
> This reverts commit 6caca443.
>
> Reason for revert: I suspect that this CL is causing https://crbug.com/890850
>
> Original change's description:
> > Enable AudioServiceSandbox flag in audio service field trial testing.
> >
> > Bug: 832666
> > Change-Id: I3ec5dbea8e34f3a9295723def845e49b2bb59af3
> > Reviewed-on: https://chromium-review.googlesource.com/1240280
> > Reviewed-by: Steven Holte <holte@chromium.org>
> > Commit-Queue: Marina Ciocea <marinaciocea@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#595397}
>
> TBR=holte@chromium.org,marinaciocea@chromium.org
>
> Change-Id: I5e6d1a9e153003c086ce8c2f247230d4832ce99b
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: 832666, 890850
> Reviewed-on: https://chromium-review.googlesource.com/1254746
> Reviewed-by: François Doray <fdoray@chromium.org>
> Commit-Queue: François Doray <fdoray@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#595464}

TBR=fdoray@chromium.org,holte@chromium.org,marinaciocea@chromium.org

Change-Id: I5176102960a7450de1b44612b85c7098d0df9c8c
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 832666, 890850
Reviewed-on: https://chromium-review.googlesource.com/1255063
Commit-Queue: Marina Ciocea <marinaciocea@chromium.org>
Reviewed-by: Marina Ciocea <marinaciocea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595475}

testing/variations/fieldtrial_testing_config.json

@@ -514,9 +514,7 @@
     "AudioService": [
         {
             "platforms": [
-                "linux",
-                "mac",
-                "windows"
+                "linux"
             ],
             "experiments": [
                 {
@@ -532,6 +530,26 @@
                 }
             ]
         },
+        {
+            "platforms": [
+                "mac",
+                "windows"
+            ],
+            "experiments": [
+                {
+                    "name": "AudioProcess_LaunchOnStartup_Sandboxed_v7",
+                    "params": {
+                        "teardown_timeout_s": "0"
+                    },
+                    "enable_features": [
+                        "AudioServiceAudioStreams",
+                        "AudioServiceLaunchOnStartup",
+                        "AudioServiceOutOfProcess",
+                        "AudioServiceSandbox"
+                    ]
+                }
+            ]
+        },
         {
             "platforms": [
                 "android",