Add TestGypXcodeNinja to run tests against the xcode-ninja generator

test/prune_targets/gyptest-prune-targets.py

Index: test/prune_targets/gyptest-prune-targets.py
diff --git a/test/prune_targets/gyptest-prune-targets.py b/test/prune_targets/gyptest-prune-targets.py
index 4f1e64a3fdf6bb52171de4536ab02de968ec96cd..e54ce6adc28f650b617842af54b05fd1f9c62685 100644
--- a/test/prune_targets/gyptest-prune-targets.py
+++ b/test/prune_targets/gyptest-prune-targets.py
@@ -11,6 +11,9 @@ Verifies --root-target removes the unnecessary targets.
 import TestGyp
 
 test = TestGyp.TestGyp()
+# The xcode-ninja generator has its own logic for which targets to include
+if test.format == 'xcode-ninja':
+  test.skip_test()
 
 build_error_code = {
   'android': 2,