[test] Use the correct precedence for choosing the build directory

This breaks looking for build output after finding valid output.
Otherwise build output with lower precedence can overwrite output
with higher precedence.

This also moves a static method.

Bug: chromium:1132088
Change-Id: I1824028243f964ab0956e54ca24921e6f32f2ca3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2440337
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Liviu Rau <liviurau@chromium.org>
Auto-Submit: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Liviu Rau <liviurau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70223}

tools/testrunner/base_runner.py

@@ -245,6 +245,24 @@ class BuildConfig(object):
     return '\n'.join(detected_options)
 
 
+def _do_load_build_config(outdir, verbose=False):
+  build_config_path = os.path.join(outdir, "v8_build_config.json")
+  if not os.path.exists(build_config_path):
+    if verbose:
+      print("Didn't find build config: %s" % build_config_path)
+    raise TestRunnerError()
+
+  with open(build_config_path) as f:
+    try:
+      build_config_json = json.load(f)
+    except Exception:  # pragma: no cover
+      print("%s exists but contains invalid json. Is your build up-to-date?"
+            % build_config_path)
+      raise TestRunnerError()
+
+  return BuildConfig(build_config_json)
+
+
 class BaseTestRunner(object):
   def __init__(self, basedir=None):
     self.basedir = basedir or BASE_DIR
@@ -419,7 +437,12 @@ class BaseTestRunner(object):
   def _load_build_config(self, options):
     for outdir in self._possible_outdirs(options):
       try:
-        self.build_config = self._do_load_build_config(outdir, options.verbose)
+        self.build_config = _do_load_build_config(outdir, options.verbose)
+
+        # In auto-detect mode the outdir is always where we found the build config.
+        # This ensures that we'll also take the build products from there.
+        self.outdir = outdir
+        break
       except TestRunnerError:
         pass
 
@@ -477,27 +500,6 @@ class BaseTestRunner(object):
       print(">>> Latest GN build found: %s" % latest_config)
       return os.path.join(DEFAULT_OUT_GN, latest_config)
 
-  def _do_load_build_config(self, outdir, verbose=False):
-    build_config_path = os.path.join(outdir, "v8_build_config.json")
-    if not os.path.exists(build_config_path):
-      if verbose:
-        print("Didn't find build config: %s" % build_config_path)
-      raise TestRunnerError()
-
-    with open(build_config_path) as f:
-      try:
-        build_config_json = json.load(f)
-      except Exception:  # pragma: no cover
-        print("%s exists but contains invalid json. Is your build up-to-date?"
-              % build_config_path)
-        raise TestRunnerError()
-
-    # In auto-detect mode the outdir is always where we found the build config.
-    # This ensures that we'll also take the build products from there.
-    self.outdir = os.path.dirname(build_config_path)
-
-    return BuildConfig(build_config_json)
-
   def _process_default_options(self, options):
     # We don't use the mode for more path-magic.
     # Therefore transform the bot mode here to fix build_config value.