Display progress as results2.html loads.
Display progress as results2.html loads.

Currently, results2.html displays "zero values" while it loads, which is a bad UX.
This change makes it display messages about what it's doing.
It updates the progress after every 100 Histograms loaded.

For a results2.html with 16k Histograms, there is still a 1500ms chunk of work as
the value-set-table organizes and displays its cells, during which the progress
does not update. In order to make the progress update during this time, the
value-set-table would need to cooperate with the HistogramImporter, probably using
tr.b.Task or something like it. This is left for another day.

Review-Url: https://chromiumcodereview.appspot.com/2429013002

benschmaus/catapult,sahiljain/catapult,catapult-project/catapult-csm,catapult-project/catapult-csm,catapult-project/catapult-csm,catapult-project/catapult,catapult-project/catapult,benschmaus/catapult,sahiljain/catapult,sahiljain/catapult,benschmaus/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult-csm,catapult-project/catapult-csm,sahiljain/catapult,catapult-project/catapult,benschmaus/catapult,benschmaus/catapult,catapult-project/catapult-csm,benschmaus/catapult,sahiljain/catapult,catapult-project/catapult-csm,benschmaus/catapult,sahiljain/catapult,catapult-project/catapult