Revert "Add 2 additional tests config in waterfalls.pyl."

This reverts commit 429c1bd74d5b821a360be6a215bcbe7c422bedeb.

Reason for revert: It breaks some CQ bots (e.g. https://ci.chromium.org/ui/p/webrtc/builders/try/linux_compile_rel/42825/overview). I am reverting to check is this is the culprit.

Original change's description:
> Add 2 additional tests config in waterfalls.pyl.
>
> * Add a presubmit check that generate_builbot_json.py has been called.
> * Add a webrtc_mixins.pyl file.
>
> Bug: webrtc:13899
> Change-Id: I7c4226ddd80bf9376bcb91476a1446a0392e7ec6
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/257904
> Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
> Commit-Queue: Jeremy Leconte <jleconte@google.com>
> Cr-Commit-Position: refs/heads/main@{#36428}

Bug: webrtc:13899
Change-Id: Ic79306688c26937a988a9eacb4799f53f7145c65
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/257919
Auto-Submit: Mirko Bonadei <mbonadei@webrtc.org>
Bot-Commit: rubber-stamper@appspot.gserviceaccount.com <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#36431}
diff --git a/infra/specs/generate_buildbot_json.py b/infra/specs/generate_buildbot_json.py
index aa03751..d625580 100755
--- a/infra/specs/generate_buildbot_json.py
+++ b/infra/specs/generate_buildbot_json.py
@@ -10,9 +10,8 @@
 ADDITIONAL_MIXINS dictonary. Calls Chromium's generate_buildbot_json.
 """
 
-import ast
+import json
 import os
-import subprocess
 import sys
 
 _SCRIPT_DIR = os.path.dirname(os.path.realpath(__file__))
@@ -23,7 +22,13 @@
 from testing.buildbot import generate_buildbot_json
 
 # Add custom mixins here.
-WEBRTC_MIXIN_FILE_NAME = os.path.join(_SCRIPT_DIR, 'mixins_webrtc.pyl')
+ADDITIONAL_MIXINS = {
+    'result_adapter': {
+        'resultdb': {
+            'result_format': 'json'
+        },
+    },
+}
 MIXIN_FILE_NAME = os.path.join(_SCRIPT_DIR, 'mixins.pyl')
 MIXINS_PYL_TEMPLATE = """\
 # GENERATED FILE - DO NOT EDIT.
@@ -42,47 +47,41 @@
 """
 
 
-def generate_mixins_file_from_used_mixins(generator):
+def main():
   chromium_args = generate_buildbot_json.BBJSONGenerator.parse_args(argv=None)
   chromium_generator = generate_buildbot_json.BBJSONGenerator(chromium_args)
   chromium_generator.load_configuration_files()
 
-  seen_mixins = set()
-  for waterfall in generator.waterfalls:
-    seen_mixins = seen_mixins.union(waterfall.get('mixins', set()))
-    for bot_name, tester in waterfall['machines'].items():
-      del bot_name
-      seen_mixins = seen_mixins.union(tester.get('mixins', set()))
-  for suite in generator.test_suites.values():
-    for test in suite.values():
-      seen_mixins = seen_mixins.union(test.get('mixins', set()))
-
-  found_mixins = ast.literal_eval(open(WEBRTC_MIXIN_FILE_NAME).read())
-  for mixin in seen_mixins:
-    if mixin not in found_mixins:
-      found_mixins[mixin] = chromium_generator.mixins[mixin]
-    elif mixin in chromium_generator.mixins:
-      assert False, '"%s" is already defined in Chromium\'s mixins.pyl' % mixin
-
-  format_data = {
-      'script_name': os.path.basename(__file__),
-      'data_source': 'mixins_webrtc.pyl and Chromium\'s mixins.pyl',
-      'mixin_data': dict(sorted(found_mixins.items())),
-  }
-  with open(MIXIN_FILE_NAME, 'w') as f:
-    f.write(MIXINS_PYL_TEMPLATE.format(**format_data))
-
-  return subprocess.call(['yapf', '-i', MIXIN_FILE_NAME])
-
-
-def main():
   override_args = ['--pyl-files-dir', _SCRIPT_DIR]
   webrtc_args = generate_buildbot_json.BBJSONGenerator.parse_args(override_args)
   webrtc_generator = generate_buildbot_json.BBJSONGenerator(webrtc_args)
   webrtc_generator.load_configuration_files()
   webrtc_generator.resolve_configuration_files()
 
-  generate_mixins_file_from_used_mixins(webrtc_generator)
+  seen_mixins = set()
+  for waterfall in webrtc_generator.waterfalls:
+    seen_mixins = seen_mixins.union(waterfall.get('mixins', set()))
+    for bot_name, tester in waterfall['machines'].items():
+      del bot_name
+      seen_mixins = seen_mixins.union(tester.get('mixins', set()))
+  for suite in webrtc_generator.test_suites.values():
+    for test in suite.values():
+      seen_mixins = seen_mixins.union(test.get('mixins', set()))
+
+  found_mixins = ADDITIONAL_MIXINS.copy()
+  for mixin in seen_mixins:
+    if mixin not in found_mixins:
+      found_mixins[mixin] = chromium_generator.mixins[mixin]
+
+  format_data = {
+      'script_name': os.path.basename(__file__),
+      'data_source': 'waterfall.pyl and Chromium\'s mixins.pyl',
+      'mixin_data': json.dumps(dict(sorted(found_mixins.items())), indent=2),
+  }
+  with open(MIXIN_FILE_NAME, 'w') as f:
+    f.write(MIXINS_PYL_TEMPLATE.format(**format_data))
+    f.close()
+
   return webrtc_generator.main()