Bug 1334829: Only run native-engine jobs from try branch. r=dustin

The 20 machines pool running taskcluster-worker is not enough to run
jobs from all branches. Let's limit these jobs to try branch while they
are tier 3.

MozReview-Commit-ID: KmkUjPp7NHL

--HG--
extra : rebase_source : 74303836d9b6550553f1b8a3a3bdbe05b893a573

taskcluster/taskgraph/transforms/tests.py

@@ -580,6 +580,15 @@ def remove_linux_pgo_try_talos(config, tests):
         yield test
 
 
+@transforms.add
+def remove_native_non_try(config, tests):
+    """Remove native-engine jobs if they are not in try branch."""
+    for test in tests:
+        if test['worker-implementation'] != 'native-engine' \
+                or config.params['project'] != 'try':
+            yield test
+
+
 @transforms.add
 def make_task_description(config, tests):
     """Convert *test* descriptions to *task* descriptions (input to