Convert content_unittests to run exclusively on Swarming

testing/buildbot/chromium.fyi.json

Index: testing/buildbot/chromium.fyi.json
diff --git a/testing/buildbot/chromium.fyi.json b/testing/buildbot/chromium.fyi.json
index ccdc54ddba78ce66452514e5a6b231b798dbba9e..edda89cb34faa306345eecb23b22f2f78b721102 100644
--- a/testing/buildbot/chromium.fyi.json
+++ b/testing/buildbot/chromium.fyi.json
@@ -16,6 +16,9 @@
           "--enable-browser-side-navigation",
           "--gtest_filter=-NavigationControllerTest.CopyRestoredStateAndNavigate:RenderFrameHostManagerTest.CancelPendingProperlyDeletesOrSwaps:RenderFrameHostManagerTest.PageDoesBackAndReload:RenderViewHostTest.ResetUnloadOnReload:ResourceDispatcherHostTest.TransferNavigationHtml:ResourceDispatcherHostTest.TransferNavigationText:ResourceDispatcherHostTest.TransferNavigationWithProcessCrash:ResourceDispatcherHostTest.TransferNavigationWithTwoRedirects:ResourceDispatcherHostTest.TransferTwoNavigationsHtml:WebContentsImplTest.CrossSiteNavigationBackPreempted:WebContentsImplTest.CrossSiteNotPreemptedDuringBeforeUnload:WebContentsImplTest.NoEarlyStop:WebContentsImplTest.ShowInterstitialCrashRendererThenGoBack:WebContentsImplTest.ShowInterstitialFromBrowserNewNavigationProceed:WebContentsImplTest.ShowInterstitialThenGoBack"
         ],
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "content_unittests"
       }
     ]
@@ -1645,6 +1648,9 @@
         "test": "content_browsertests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "content_unittests"
       },
       {
@@ -1769,6 +1775,9 @@
         "test": "content_browsertests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "content_unittests"
       },
       {
@@ -2825,6 +2834,9 @@
         "test": "content_browsertests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "content_unittests"
       },
       {
@@ -3197,6 +3209,9 @@
         "test": "content_browsertests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "content_unittests"
       },
       {