Use a faster rolling fixed Clang revision for ASan on Windows

We want a fixed Clang revision for ASan on Windows because ClusterFuzz
produces archived builds.  We don't want Clang to change underfoot and
produce a bad Chromium build that gets archived.

Long term, when ASan for Windows stabilizes, we should remove this
extra fixed revision and use the mainline Chromium revision.  For now,
we don't build with -Werror with Clang on Windows, so it isn't as
important to be in sync with other platforms.

R=thakis@chromium.org
BUG=82385, 345874
NOTRY=true

Review URL: https://codereview.chromium.org/341963002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@278271 0039d316-1c4b-4281-b951-d872f2087c98

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, '..', '..', '..'))