Revert of roll clang 254049:254793

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 3f70c6c56c2f77d14ef2702b2e0139e7b73ba800..db7df2ac8e97b9239a105211c25e168e83db3590 100755
--- a/tools/clang/scripts/update.py
+++ b/tools/clang/scripts/update.py
@@ -8,6 +8,7 @@
 It is also used by package.py to build the prebuilt clang binaries."""
 
 import argparse
+import cStringIO
 import distutils.spawn
 import glob
 import os
@@ -19,13 +20,14 @@
 import sys
 import tarfile
 import tempfile
+import time
 import urllib2
 import zipfile
 
 # 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.
-CLANG_REVISION = '254793'
+CLANG_REVISION = '254049'
 
 use_head_revision = 'LLVM_FORCE_HEAD_REVISION' in os.environ
 if use_head_revision:
@@ -514,6 +516,10 @@
     cflags += ['-DLLVM_FORCE_HEAD_REVISION']
     cxxflags += ['-DLLVM_FORCE_HEAD_REVISION']
 
+  # Pin MSan to the old ABI.
+  # TODO(eugenis): Remove when MSan migrates to new ABI (crbug.com/560589).
+  cxxflags += [ '-DMSAN_LINUX_X86_64_OLD_MAPPING' ]
+
   CreateChromeToolsShim()
 
   deployment_env = None