Don't share ResourceDispatcherHostImpl's timer for reporting upload progress.

We want that timer to run only when needed, which is when a tab is loading,
or currently when there is an upload in progress. This change separates the
upload progress logic to make things simpler and help towards that goal.

BUG=483287

Review URL: https://codereview.chromium.org/1130343006

Cr-Commit-Position: refs/heads/master@{#331228}
5 files changed