It appears that the binary private key for origin trials testing was corrupted on its way through code review and the commit queue.

The file appears to have suffered from base64 encoding, and then truncation at the first 0x0d (translated to 0x0a for your convenience). The end result is 12 incorrect bytes in place of 64 correct ones.

The correct key, as specified in code comments, should be the following 64 bytes:

  0x83, 0x67, 0xf4, 0xcd, 0x2a, 0x1f, 0x0e, 0x04, 0x0d, 0x43, 0x13,
  0x4c, 0x67, 0xc4, 0xf4, 0x28, 0xc9, 0x90, 0x15, 0x02, 0xe2, 0xba,
  0xfd, 0xbb, 0xfa, 0xbc, 0x92, 0x76, 0x8a, 0x2c, 0x4b, 0xc7, 0x75,
  0x10, 0xac, 0xf9, 0x3a, 0x1c, 0xb8, 0xa9, 0x28, 0x70, 0xd2, 0x9a,
  0xd0, 0x0b, 0x59, 0xe1, 0xac, 0x2b, 0xb7, 0xd5, 0xca, 0x1f, 0x64,
  0x90, 0x08, 0x8e, 0xa8, 0xe0, 0x56, 0x3a, 0x04, 0xd0

(This was previously reported in a comment to https://bugs.chromium.org/p/chromium/issues/detail?id=557512, but never revisited after the file was actually committed, until now.)