Simplify SkInstCnt

This code requires fewer macros to use it (just one), has less code in macro
definitions, and has simpler synchronization code (just atomic ints, no SkOnce,
no SkMutex, etc.)

A minor downside, we lose indentation and reverse-ordering in the final report:
  Leaked SkRefCntBase: 7
     Leaked SkFontMgr: 1
     Leaked SkWeakRefCnt: 1
         Leaked SkTypeface: 1
     Leaked SkFlattenable: 3
         Leaked SkXfermode: 3
     Leaked SkPathRef: 1
     Leaked SkPixelRef: 1
         Leaked SkMallocPixelRef: 1
becomes
  Leaked SkXfermode: 3
  Leaked SkMallocPixelRef: 1
  Leaked SkPixelRef: 1
  Leaked SkPathRef: 1
  Leaked SkFlattenable: 3
  Leaked SkTypeface: 1
  Leaked SkWeakRefCnt: 1
  Leaked SkFontMgr: 1
  Leaked SkRefCntBase: 7

This is motivated by wanting to land https://codereview.chromium.org/806473006/,
which makes sure all static use of SkOnce are in global scope.  The current
implementation of SkInstCnt uses them in function scope, which isn't safe.
BUG=skia:

No public API changes.
TBR=reed@google.com

Review URL: https://codereview.chromium.org/841263004
13 files changed