Add debug-only helper methods to get #ops & #clips per opList

These are being/will be used to determine the correct amout of memory to preallocate for ops & clips in the opLists.

Change-Id: I98ebaec8a6e72a43d97101aca5fbc58264964ebd
Reviewed-on: https://skia-review.googlesource.com/15882
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
7 files changed