Don't call WebContents::DownloadImage() callback if the WebContents were deleted

BUG=583718

Review URL: https://codereview.chromium.org/1685343004

Cr-Commit-Position: refs/heads/master@{#375700}
bool WebContentsImpl::IsCrashed() const {
  return (crashed_status_ == base::TERMINATION_STATUS_PROCESS_CRASHED ||
          crashed_status_ == base::TERMINATION_STATUS_ABNORMAL_TERMINATION ||
          crashed_status_ == base::TERMINATION_STATUS_PROCESS_WAS_KILLED ||
#if defined(OS_CHROMEOS)
          crashed_status_ ==
              base::TERMINATION_STATUS_PROCESS_WAS_KILLED_BY_OOM ||
#endif
          crashed_status_ == base::TERMINATION_STATUS_LAUNCH_FAILED
          );
}

bool WebContentsImpl::IsCrashed() const {
  return (crashed_status_ == base::TERMINATION_STATUS_PROCESS_CRASHED ||
          crashed_status_ == base::TERMINATION_STATUS_ABNORMAL_TERMINATION ||
          crashed_status_ == base::TERMINATION_STATUS_PROCESS_WAS_KILLED ||
#if defined(OS_CHROMEOS)
          crashed_status_ ==
              base::TERMINATION_STATUS_PROCESS_WAS_KILLED_BY_OOM ||
#endif
          crashed_status_ == base::TERMINATION_STATUS_LAUNCH_FAILED
          );
}
