upload_symbols: add logging whenever we dedupe a symbol

Add a bit of debug info to try and help track down the upload hang.

BUG=chromium:355843
TEST=`./buildbot/run_tests` passes

Change-Id: I8bc3a2c3fd65ee960edefc61ef5e0fe01c65fad0
Reviewed-on: https://chromium-review.googlesource.com/195770
Reviewed-by: Don Garrett <dgarrett@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
1 file changed