Add simple depends_on API.

recipes/top.py

+from recipe_engine.recipe_api import Property
+from recipe_engine import config
+
+DEPS = [
+    'recipe_engine/properties',
+]
+
+PROPERTIES = {
+    'to_pass': Property(),
+}
+
+RETURN_SCHEMA = config.ReturnSchema(
+    result=config.Single(int),
+)
+
+def RunSteps(api, to_pass):
+  res = api.depend_on('bottom', {'number': to_pass})

[estaab, 2015/11/10 02:55:12]

Since to_pass is just a plain Property() does that mean it doesn't have a type?
Is it valid to pass this directly into bottom which takes an int property type?

[martiniss, 2015/11/13 00:17:12]

Technically yes, and naive simulation tests won't catch this. We would need to
add static analysis to our python programs, which I guess we could do.

More advanced simulation tests would catch it though, because the recipe api
would realize that you're passing in a bad type.

+  return RETURN_SCHEMA(**res)

[estaab, 2015/11/10 02:55:12]

Would "return {'result': res['result']}" also be valid here?

[martiniss, 2015/11/13 00:17:12]

Yes.

+
+def GenTests(api):
+  yield (
+      api.test('basic') +
+      api.properties(to_pass=3)
+  )