upload_symbols: add logging whenever we dedupe a symbol
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 <546ec366615570e68497e3c5df9092106a9808f4@chromium.org>
Commit-Queue: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@chromium.org>
Tested-by: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@chromium.org>

chadversary/chromiumos.chromite,bpsinc-native/src_third_party_chromite,bpsinc-native/src_third_party_chromite,chadversary/chromiumos.chromite,bpsinc-native/src_third_party_chromite