Add json test results format support for SwarmingIsolatedScriptTest

scripts/slave/recipe_modules/swarming/__init__.py

Index: scripts/slave/recipe_modules/swarming/__init__.py
diff --git a/scripts/slave/recipe_modules/swarming/__init__.py b/scripts/slave/recipe_modules/swarming/__init__.py
index 553fdfced77d7737e2314540b2acaf165542ba56..be89ecb3af7f9606172f8a6c2d79fbda32398781 100644
--- a/scripts/slave/recipe_modules/swarming/__init__.py
+++ b/scripts/slave/recipe_modules/swarming/__init__.py
@@ -15,9 +15,15 @@ DEPS = [
   'test_utils',
 ]
 
-from recipe_engine.recipe_api import Property
+try:
+  from recipe_engine.recipe_api import Property
 
-PROPERTIES = {
-  'show_shards_in_collect_step': Property(default=False, kind=bool),
-  'show_isolated_out_in_collect_step': Property(default=True, kind=bool),
-}
+  PROPERTIES = {
+    'show_shards_in_collect_step': Property(default=False, kind=bool),
+    'show_isolated_out_in_collect_step': Property(default=True, kind=bool),
+  }
+# When results_merger_unittest is run, these import will raise exception due
+# to recipe_engine not found. We just handle the ImportError gracefully to
+# let results_merger_unittest runnable.
+except ImportError:  # pragma: no cover
+  pass