buildbucket response's 'failure_reason': 'BUILD_FAILURE' does not necessarily mean "Compile failed unexpectedly."

In the case of https://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_variable/builds/74, a swarming task was triggered twice resulting in a subsequent exception.

However the error reported by the dashboard says 'Compile failed expectedly'

Instead 'BUILD_FAILURE' should be treated as a general failure and is not compile-specific.