Avoid computing patch_root in get_files_affected_by_patch.

recipe_modules/gclient/example.py

Index: recipe_modules/gclient/example.py
diff --git a/recipe_modules/gclient/example.py b/recipe_modules/gclient/example.py
index fa6daf8950862ab8c919bf525932360496efa0a9..2f7bb93d13994dd3cf5c3e51ccccf9357f634511 100644
--- a/recipe_modules/gclient/example.py
+++ b/recipe_modules/gclient/example.py
@@ -6,6 +6,7 @@ DEPS = [
   'gclient',
   'recipe_engine/path',
   'recipe_engine/properties',
+  'recipe_engine/platform',
 ]
 
 
@@ -92,6 +93,7 @@ def RunSteps(api):
   assert not api.gclient.is_blink_mode
 
 
+
 def GenTests(api):
   yield api.test('basic')