DM tweaks

 - Don't print status updates for skipped tasks or count them as pending tasks.
 - Refactor DMReporter a bit for better symmetry, be more explicit about
   how we read atomics (that is, approximately) in printStatus() (née finish()).
 - Remove mutex locking from printStatus().

BUG=skia:
R=halcanary@google.com, mtklein@google.com

Author: mtklein@chromium.org

Review URL: https://codereview.chromium.org/309483003

git-svn-id: http://skia.googlecode.com/svn/trunk@14977 2bbb7eff-a529-9590-31e7-b0007b416f81
5 files changed