Use a faster rolling fixed Clang revision for ASan on Windows

tools/clang/scripts/update.py

Index: tools/clang/scripts/update.py
diff --git a/tools/clang/scripts/update.py b/tools/clang/scripts/update.py
index d0ba8830786cddd1699791954969c93757b118de..89c5b1f1787884af8c2c7f5f8c6af3002e1ad57d 100755
--- a/tools/clang/scripts/update.py
+++ b/tools/clang/scripts/update.py
@@ -18,6 +18,12 @@ import sys
 # Note: this revision is only used for Windows. Other platforms use update.sh.
 LLVM_WIN_REVISION = 'HEAD'
 
+# ASan on Windows is useful enough to use it even while the clang/win is still
+# in bringup. Use a pinned revision to make it slightly more stable.
+if (sys.platform in ['win32', 'cygwin'] and
+    re.search(r'\b(asan)=1', os.environ.get('GYP_DEFINES', ''))):
+  LLVM_WIN_REVISION = '210586'
+
 # Path constants. (All of these should be absolute paths.)
 THIS_DIR = os.path.abspath(os.path.dirname(__file__))
 CHROMIUM_DIR = os.path.abspath(os.path.join(THIS_DIR, '..', '..', '..'))