Remove build directory before performing perf tryjob.

scripts/slave/recipe_modules/perf_try/api.py

Index: scripts/slave/recipe_modules/perf_try/api.py
diff --git a/scripts/slave/recipe_modules/perf_try/api.py b/scripts/slave/recipe_modules/perf_try/api.py
index f60354448b09f2b5798a9bf752aa96030d67c549..50758b1e3c668ce3294f01194810eeedd424e9ab 100644
--- a/scripts/slave/recipe_modules/perf_try/api.py
+++ b/scripts/slave/recipe_modules/perf_try/api.py
@@ -183,6 +183,13 @@ class PerfTryJobApi(recipe_api.RecipeApi):
       self.m.chromium.cleanup_temp()
 
     if 'With Patch' in name:
+      # We've had some cases where a stale build directory was used on perf try job,
+      # leading to unwanted cache and temp data. The best way to ensure
+      # the old build directory is removed before doing any compilation.
+      self.m.file.rmtree(
+        'build directory',
+        self.m.chromium.c.build_dir.join(self.m.chromium.c.build_config_fs))
+
       self.m.chromium_tests.transient_check(
           update_step,
           lambda transform_name: self.m.chromium_tests.run_mb_and_compile(
@@ -200,9 +207,6 @@ class PerfTryJobApi(recipe_api.RecipeApi):
     if (not kwargs.get('allow_flakes', True) and
         cfg.get('test_type', 'perf') != 'return_code'):
       overall_success = all(v == 0 for v in retcodes)
-    if not overall_success:  # pragma: no cover
-      raise self.m.step.StepFailure(
-          'Patched version failed to run performance test.')
     return {
         'results': all_values,
         'ret_code': overall_success,