Add --site-per-process flavor of //content tests to Site Isolation Android bot.

content/test/BUILD.gn

Index: content/test/BUILD.gn
diff --git a/content/test/BUILD.gn b/content/test/BUILD.gn
index 685d15570d43280fb066f18941be17538d311f3e..e22558f3286d85f4533f541aaec99082b3ba6fa5 100644
--- a/content/test/BUILD.gn
+++ b/content/test/BUILD.gn
@@ -669,7 +669,7 @@ test("content_browsertests") {
         data += [ "//testing/buildbot/filters/browser-side-navigation.linux.content_browsertests.filter" ]
       }
 
-      if (is_win || is_linux) {
+      if (is_win || is_linux || is_android) {
         data += [ "//testing/buildbot/filters/site-per-process.content_browsertests.filter" ]
       }
     }