A build failure [1] was caused by the toolchain roll [2]. I've rolled out the patch to green the tree [3].

[1] https://build.chromium.org/p/chromium.mac/builders/Mac10.10%20Tests/builds/19709

dyld: Library not loaded: /usr/lib/libcompression.dylib
  Referenced from: /b/c/b/Mac10_10_Tests/src/build/mac_files/Xcode.app/Contents/SharedFrameworks/DTXConnectionServices.framework/Versions/A/DTXConnectionServices
  Reason: image not found
Failed to download toolchain toolchain-8E2002-3.tgz.
Exception Command '['sudo', '/usr/bin/xcodebuild', '-license', 'accept']' returned non-zero exit status 133
Exiting.
Error: Command '/usr/bin/python src/build/mac_toolchain.py' returned non-zero exit status 1 in /b/c/b/Mac10_10_Tests
Hook '/usr/bin/python src/build/mac_toolchain.py' took 54.11 secs
step returned non-zero exit code: 2

[2] https://codereview.chromium.org/2941293003/
[3] https://codereview.chromium.org/2946133002/