Fix swarming for content_browsertests and browser_tests on site isolation bots.

content/test/BUILD.gn

Index: content/test/BUILD.gn
diff --git a/content/test/BUILD.gn b/content/test/BUILD.gn
index c36e8d06642b4c947c33bc01259211573111211a..e5ca431e68ea15b31fd5d53e5133600bb128126f 100644
--- a/content/test/BUILD.gn
+++ b/content/test/BUILD.gn
@@ -676,6 +676,10 @@ test("content_browsertests") {
       if (is_linux) {
         data += [ "//testing/buildbot/filters/browser-side-navigation.linux.content_browsertests.filter" ]
       }
+
+      if (is_win || is_linux) {
+        data += [ "//testing/buildbot/filters/site-per-process.content_browsertests.filter" ]
+      }
     }
   }