Fix include path for moved thread_task_runner_handle.h header in blimp/

Also fix presubmit error in engine_authentication_handler_unittest.cc for using
static string instead of const char[]

BUG=610438
TBR=kmarshall@chromium.org

Review-Url: https://codereview.chromium.org/1968113002
Cr-Commit-Position: refs/heads/master@{#392974}
9 files changed