Use rmdir /s/q instead of flaky shutil.rmtree on Windows

build/clobber.py

Index: build/clobber.py
diff --git a/build/clobber.py b/build/clobber.py
index 785011a171d836f9cbf8dc0ddd101a015b3335de..c05f524ee28ce93c8d94c7fc3974bf2a3707c934 100755
--- a/build/clobber.py
+++ b/build/clobber.py
@@ -8,6 +8,7 @@
 import argparse
 import os
 import shutil
+import subprocess
 import sys
 
 
@@ -35,11 +36,20 @@ def extract_gn_build_commands(build_ninja_file):
   return result
 
 
+def delete_dir(build_dir):
+  # For unknown reasons (anti-virus?) rmtree of Chromium build directories
+  # often fails on Windows.
+  if sys.platform.startswith('win'):
+    subprocess.check_call(['rmdir', '/s', '/q', build_dir], shell=True)
+  else:
+    shutil.rmtree(build_dir)
+
+
 def delete_build_dir(build_dir):
   # GN writes a build.ninja.d file. Note that not all GN builds have args.gn.
   build_ninja_d_file = os.path.join(build_dir, 'build.ninja.d')
   if not os.path.exists(build_ninja_d_file):
-    shutil.rmtree(build_dir)
+    delete_dir(build_dir)
     return
 
   # GN builds aren't automatically regenerated when you sync. To avoid
@@ -56,7 +66,7 @@ def delete_build_dir(build_dir):
   except IOError:
     args_contents = ''
 
-  shutil.rmtree(build_dir)
+  delete_dir(build_dir)
 
   # Put back the args file (if any).
   os.mkdir(build_dir)