Convert sandbox_mac_unittests to run exclusively on Swarming

testing/buildbot/chromium.fyi.json

 {
   "Browser Side Navigation Linux": {
     "gtest_tests": [
       {
         "args": [
           "--enable-browser-side-navigation",
           "--gtest_filter=-CrossSiteRedirectorBrowserTest.VerifyCrossSiteRedirectURL:CrossSiteTransferTest.NoLeakOnCrossSiteCancel:CrossSiteTransferTest.ReplaceEntryCrossProcessThenTransfer:CrossSiteTransferTest.ReplaceEntryCrossProcessTwice:CrossSiteTransferTest.ReplaceEntryInProcessThenTranfers:DevToolsProtocolTest.NavigationPreservesMessages:NavigationControllerBrowserTest.CorrectLengthWithCurrentItemReplacement:NavigationControllerBrowserTest.FrameNavigationEntry_BlankAutoSubframe:NavigationControllerBrowserTest.NavigationTypeClassification_ClientSideRedirect:NavigationControllerBrowserTest.NavigationTypeClassification_ExistingPage:NavigationControllerBrowserTest.NavigationTypeClassification_InPage:NavigationControllerBrowserTest.NavigationTypeClassification_NewAndAutoSubframe:NavigationControllerBrowserTest.NavigationTypeClassification_NewPage:NavigationControllerBrowserTest.PreventSpoofFromSubframeAndReplace:NavigationControllerBrowserTest.StopCausesFailureDespiteJavaScriptURL:RenderViewImplTest.DecideNavigationPolicy:RenderViewImplTest.NavigationStartOverride:RenderViewImplTest.OnNavigationHttpPost:RenderViewImplTest.ReloadWhileSwappedOut:RenderViewImplTest.TestBackForward:SecurityExploitBrowserTest.AttemptDuplicateRenderViewHost:SecurityExploitBrowserTest.AttemptDuplicateRenderWidgetHost:SecurityExploitBrowserTest.InterstitialCommandFromUnderlyingContent:ServiceWorkerBrowserTest.CrossSiteTransfer:ServiceWorkerBrowserTest.ImportsBustMemcache:ServiceWorkerBrowserTest.Reload:ServiceWorkerBrowserTest.ResponseFromHTTPServiceWorkerIsNotMarkedAsSecure:ServiceWorkerBrowserTest.ResponseFromHTTPSServiceWorkerIsMarkedAsSecure:SessionHistoryTest.CrossFrameFormBackForward:SessionHistoryTest.FrameBackForward:SessionHistoryTest.FrameFormBackForward:SessionHistoryTest.LocationChangeInSubframe:SitePerProcessBrowserTest.CrossSiteDidStopLoading:WebContentsImplBrowserTest.ClearNonVisiblePendingOnFail:WebContentsViewAuraTest.ReplaceStateReloadPushState:WebRtcBrowserTest.CallInsideIframe:WebUIMojoTest.EndToEndPing"
         ],
         "swarming": {
           "can_use_on_swarming_builders": true
@@ skipping 602 matching lines @@
       {
         "test": "ppapi_unittests"
       },
       {
         "test": "printing_unittests"
       },
       {
         "test": "remoting_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "sandbox_mac_unittests"
       },
       {
         "test": "skia_unittests"
       },
       {
         "test": "sql_unittests"
       },
       {
         "test": "sync_integration_tests"
@@ skipping 148 matching lines @@
       {
         "test": "ppapi_unittests"
       },
       {
         "test": "printing_unittests"
       },
       {
         "test": "remoting_unittests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "sandbox_mac_unittests"
       },
       {
         "test": "skia_unittests"
       },
       {
         "test": "sql_unittests"
       },
       {
         "test": "sync_integration_tests"
@@ skipping 3005 matching lines @@
       },
       {
         "args": [
           "--site-per-process"
         ],
         "test": "unit_tests"
       }
     ]
   }
 }