[telemetry] Upload to Cloud Storage OnUpload instead of OnCommit.

Also includes new unit tests. 97% of this patch is unit test work, only 3 lines in the actual fix.


BUG=309865
TEST=tools/perf/run_tests Presubmit

Review URL: https://codereview.chromium.org/34413009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230346 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 230346