Skip ElfCoreDumpTest.ValidCoreFile test if no core dump is generated.

This CL is cherry-picked from upstream:
  http://breakpad.appspot.com/342001

CrashGenerator::CreateChildCrash() may have some flakiness. This patch
changes ElfCoreDumpTest to temporarily skip the ValidCoreFile test if
no core dump is generated by CrashGenerator::CreateChildCrash(), but
print out the error message to help debug the flakiness.

BUG=chromium-os:24982
TEST=Tested the following:
1. Build on 32-bit and 64-bit Linux with gcc 4.6.
2. All unit tests pass.

Change-Id: I7d6a5c1e0404d2c87b108207ef6aae6e4640bb47
Reviewed-on: https://gerrit.chromium.org/gerrit/14014
Tested-by: Ben Chan <benchan@chromium.org>
Commit-Ready: Ben Chan <benchan@chromium.org>
Reviewed-by: Michael Krebs <mkrebs@chromium.org>
2 files changed