I have encountered a number of cases recently where build failures encountered by EWS were not able to be diagnosed from the build logs because Visual Studio produces so much output that the relevant error messages were not contained within the first 500 characters of logging. For example, in <https://webkit-queues.appspot.com/results/5200799210668032> we have an EWS failure that contains a log file with no errors. It simply contains a series of "Build succeeded" messages, followed by a "Build Failed" with no explanation.
Another good example: <https://webkit-queues.appspot.com/results/6313512225734656>. How can anyone tell what's wrong?
This problem may be largely resolved by Bug 140845, since we can pass the "/verbosity:minimal" flag to MSBuild.