depot_tools: Always use depot_tools .vpython to execute presubmit recipes.

presubmit_support.py should correctly find and use .vpython files.
This will prevent issues like https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/1874458

Bug: 1002153
Change-Id: I677f40b1fd2c436867cb5c6cbdeaff0d16f33a2f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1874892Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>

recipes/README.recipes.md

@@ -757,7 +757,7 @@ Raises:
 
 Return a presubmit step.
 
-— **def [execute](/recipes/recipe_modules/presubmit/api.py#74)(self, bot_update_step):**
+— **def [execute](/recipes/recipe_modules/presubmit/api.py#75)(self, bot_update_step):**
 
 Runs presubmit and sets summary markdown if applicable.
 
@@ -766,7 +766,7 @@ Args:
 Returns:
   a RawResult object, suitable for being returned from RunSteps.
 
-— **def [prepare](/recipes/recipe_modules/presubmit/api.py#39)(self):**
+— **def [prepare](/recipes/recipe_modules/presubmit/api.py#40)(self):**
 
 Set up a presubmit run.
 

recipes/recipe_modules/presubmit/api.py

@@ -27,6 +27,7 @@ class PresubmitApi(recipe_api.RecipeApi):
   def __call__(self, *args, **kwargs):
     """Return a presubmit step."""
 
+    kwargs['venv'] = True
     name = kwargs.pop('name', 'presubmit')
     with self.m.depot_tools.on_path():
       presubmit_args = list(args) + [
@@ -106,16 +107,10 @@ class PresubmitApi(recipe_api.RecipeApi):
       '--upstream', upstream,  # '' if not in bot_update mode.
     ])
 
-    venv = True
-    # TODO(iannucci): verify that presubmit_support.py correctly finds and
-    # uses .vpython files, then remove this configuration.
-    if self._vpython_spec_path:
-      venv = abs_root.join(self._vpython_spec_path)
-
     raw_result = result_pb2.RawResult()
     step_json = self(
         *presubmit_args,
-        venv=venv, timeout=self._timeout_s,
+        timeout=self._timeout_s,
         # ok_ret='any' causes all exceptions to be ignored in this step
         ok_ret='any')
     # Set recipe result values

recipes/recipe_modules/presubmit/examples/full.expected/basic.json

 [
   {
     "cmd": [
-      "python",
+      "vpython",
       "-u",
       "RECIPE_REPO[depot_tools]/presubmit_support.py",
       "--json_output",