Rework crash handling in run-webkit-tests under sanitizers.

When running under a sanitizer like ASAN, we weren't very smart
about how we handled errors.

First, we didn't actually write out the error information.

Second, we would look for a breakpad dump and overwrite a crash log
generated by ASAN.

Third, we would use addr2line instead of llvm-symbolizer, and the latter
is much faster.

This patch corrects all of these issues.

R=jochen@chromium.org, glider@chromium.org, earthdok@chromium.org
BUG=402051

Review URL: https://codereview.chromium.org/567333004

git-svn-id: svn://svn.chromium.org/blink/trunk@182173 bbb929c8-8fbe-4397-9dbb-9b2b20218538