reland "make bots call android_ninja instead of android_make"

slave/skia_slave_scripts/build_step.py

Index: slave/skia_slave_scripts/build_step.py
diff --git a/slave/skia_slave_scripts/build_step.py b/slave/skia_slave_scripts/build_step.py
index 80089b3bbecdfe0ea8c3a451f01d9d6860685f08..ca1f6e4390b2913ad0a468f513bc585cbdda86bf 100644
--- a/slave/skia_slave_scripts/build_step.py
+++ b/slave/skia_slave_scripts/build_step.py
@@ -191,10 +191,12 @@ class BuildStep(multiprocessing.Process):
 
     if os.name == 'nt':
       self._default_make_flags = []
+      self._default_ninja_flags = []
     else:
       # Set the jobs limit to 4, since we have multiple slaves running on each
       # machine.
       self._default_make_flags = ['--jobs', '4', '--max-load=4.0']
+      self._default_ninja_flags = ['-j', '4', '-l', '4.0']
 
     # Adding the playback directory transfer objects.
     self._local_playback_dirs = LocalSkpPlaybackDirs(
@@ -244,11 +246,16 @@ class BuildStep(multiprocessing.Process):
   def args(self):
     return self._args
 
+  # TODO(epoger): remove default_make_flags property once all builds use ninja
   @property
   def default_make_flags(self):
     return self._default_make_flags
 
   @property
+  def default_ninja_flags(self):
+    return self._default_ninja_flags
+
+  @property
   def make_flags(self):
     return self._make_flags