Failing from https://uberchromegw.corp.google.com/i/chromeos/builders/smaug-paladin/builds/3105:

Total: 528 packages (528 new, 456 binaries), Size of downloads: 1110241 KiB
Conflict: 1 block (1 unsatisfied)

 * Error: The above package list contains packages which cannot be
 * installed at the same time on the same system.

  (sys-fs/udev-208-r6:0/0::chromiumos, binary scheduled for merge to '/build/smaug/') pulled in by
    >=sys-fs/udev-208-r1:0/0[abi_x86_32(-)?,abi_x86_64(-)?,abi_x86_x32(-)?,abi_mips_n32(-)?,abi_mips_n64(-)?,abi_mips_o32(-)?,abi_ppc_32(-)?,abi_ppc_64(-)?,abi_s390_32(-)?,abi_s390_64(-)?,static-libs?] (>=sys-fs/udev-208-r1:0/0) required by (virtual/libudev-215-r1:0/1::portage-stable, ebuild scheduled for merge to '/build/smaug/')
    >=sys-fs/udev-208-r1 required by (virtual/udev-215:0/0::portage-stable, binary scheduled for merge to '/build/smaug/')

  (dev-libs/libgudev-230:0/0::portage-stable, ebuild scheduled for merge to '/build/smaug/') pulled in by
    dev-libs/libgudev:0/0 required by (virtual/libgudev-215-r3:0/0::portage-stable, binary scheduled for merge to '/build/smaug/')


For more information about Blocked Packages, please refer to the following
section of the Gentoo Linux x86 Handbook (architecture is irrelevant):

http://www.gentoo.org/doc/en/handbook/handbook-x86.xml?full=1#blocked

I don't see any commit that could explain the failure.

P0: Blocking the CQ.