quipper: Restore perf_converter to buildable state.

Add DCHECK to mybase, and add scoped_temp_path.cc to Makefile.external.

BUG=chromium:378921
TEST=make -f Makefile.external perf_converter

Change-Id: I8e488ff3624eb974c8f6246a35fea8d26ec9e9ac
Reviewed-on: https://chromium-review.googlesource.com/202516
Reviewed-by: Simon Que <sque@chromium.org>
Tested-by: David Sharp <dhsharp@chromium.org>
Commit-Queue: David Sharp <dhsharp@chromium.org>
2 files changed