[infra] Fix clang-format invocation from git cl format

tools/buildtools/update.py

Index: tools/buildtools/update.py
diff --git a/tools/buildtools/update.py b/tools/buildtools/update.py
index 6d676293aa43f3d1b1112c82f05cc6caa84c9e41..2f9b4b8a8b1aa591d02bbd503c3cc53e773bf902 100755
--- a/tools/buildtools/update.py
+++ b/tools/buildtools/update.py
@@ -14,6 +14,7 @@ THIS_DIR = os.path.abspath(os.path.dirname(__file__))
 DART_ROOT = os.path.abspath(os.path.join(THIS_DIR, '..', '..'))
 BUILDTOOLS = os.path.join(DART_ROOT, 'buildtools')
 TOOLS_BUILDTOOLS = os.path.join(DART_ROOT, 'tools', 'buildtools')
+TOOLCHAIN = os.path.join(BUILDTOOLS, 'toolchain')
 
 sys.path.insert(0, os.path.join(DART_ROOT, 'tools'))
 import find_depot_tools
@@ -23,12 +24,14 @@ DEPOT_PATH = find_depot_tools.add_depot_tools_to_path()
 
 def Update():
   path = os.path.join(BUILDTOOLS, 'update.sh')
-  return subprocess.call(['/bin/bash', path, '--toolchain', '--gn'], cwd=DART_ROOT)
+  command = ['/bin/bash', path, '--toolchain', '--gn']
+  return subprocess.call(command, cwd=DART_ROOT)
 
 
 def UpdateGNOnWindows():
   sha1_file = os.path.join(BUILDTOOLS, 'win', 'gn.exe.sha1')
-  downloader_script = os.path.join(DEPOT_PATH, 'download_from_google_storage.py')
+  downloader_script = os.path.join(
+      DEPOT_PATH, 'download_from_google_storage.py')
   download_cmd = [
     'python',
     downloader_script,
@@ -47,7 +50,8 @@ def UpdateGNOnWindows():
 def UpdateClangFormatOnWindows():
   sha1_file = os.path.join(TOOLS_BUILDTOOLS, 'win', 'clang-format.exe.sha1')
   output_dir = os.path.join(BUILDTOOLS, 'win', 'clang-format.exe')
-  downloader_script = os.path.join(DEPOT_PATH, 'download_from_google_storage.py')
+  downloader_script = os.path.join(
+      DEPOT_PATH, 'download_from_google_storage.py')
   download_cmd = [
     'python',
     downloader_script,
@@ -65,13 +69,24 @@ def UpdateClangFormatOnWindows():
   return subprocess.call(download_cmd)
 
 
-def CopyClangFormatScripts():
-  linux_script = os.path.join(TOOLS_BUILDTOOLS, 'linux64', 'clang-format')
-  mac_script = os.path.join(TOOLS_BUILDTOOLS, 'mac', 'clang-format')
-  linux_dest = os.path.join(BUILDTOOLS, 'linux64', 'clang-format')
-  mac_dest = os.path.join(BUILDTOOLS, 'mac', 'clang-format')
-  shutil.copy2(linux_script, linux_dest)
-  shutil.copy2(mac_script, mac_dest)
+# On Mac and Linux we copy clang-format to the place where git cl format
+# expects it to be.
+def CopyClangFormat():
+  if sys.platform == 'darwin':
+    platform = 'darwin'
+    subdir = 'mac'
+  elif sys.platform.startswith('linux'):
+    platform = 'linux'
+    subdir = 'linux64'
+  else:
+    print 'Unknown platform: ' + sys.platform
+    return 1
+
+  clang_format = os.path.join(
+      TOOLCHAIN, 'clang+llvm-x86_64-' + platform, 'bin', 'clang-format')
+  dest = os.path.join(BUILDTOOLS, subdir, 'clang-format')
+  shutil.copy2(clang_format, dest)
+  return 0
 
 
 def main(argv):
@@ -80,8 +95,9 @@ def main(argv):
     if result != 0:
       return result
     return UpdateClangFormatOnWindows()
-  CopyClangFormatScripts()
-  return Update()
+  if Update() != 0:
+    return 1
+  return CopyClangFormat()
 
 
 if __name__ == '__main__':