Pick a fixed Clang revision for Windows now that we have an LKGR ASan builder

This way, the LKGR builder and the developers who want to try ASan (or just Clang) on Windows won't get a broken Clang revision.

The FYI bots got LLVM_WIN_REVISION=HEAD in r276301 so won't be affected.

BUG=82385,345874
NOTRY=true

Review URL: https://codereview.chromium.org/320383004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@276366 0039d316-1c4b-4281-b951-d872f2087c98

tools/clang/scripts/update.py

@@ -15,8 +15,9 @@ import sys
 # Do NOT CHANGE this if you don't know what you're doing -- see
 # https://code.google.com/p/chromium/wiki/UpdatingClang
 # Reverting problematic clang rolls is safe, though.
+# TODO(hans): update the wiki to cover Windows when Clang is stable enough.
 # Note: this revision is only used for Windows. Other platforms use update.sh.
-LLVM_WIN_REVISION = 'HEAD'
+LLVM_WIN_REVISION = os.environ.get('LLVM_WIN_REVISION', '210586')
 
 # Path constants. (All of these should be absolute paths.)
 THIS_DIR = os.path.abspath(os.path.dirname(__file__))
@@ -29,9 +30,8 @@ CLANG_DIR = os.path.join(LLVM_DIR, 'tools', 'clang')
 COMPILER_RT_DIR = os.path.join(LLVM_DIR, 'projects', 'compiler-rt')
 STAMP_FILE = os.path.join(LLVM_BUILD_DIR, 'cr_build_revision')
 
-LLVM_REPO_URL='https://llvm.org/svn/llvm-project'
-if 'LLVM_REPO_URL' in os.environ:
-  LLVM_REPO_URL = os.environ['LLVM_REPO_URL']
+LLVM_REPO_URL = os.environ.get('LLVM_REPO_URL',
+                               'https://llvm.org/svn/llvm-project')
 
 
 def ReadStampFile():