Split SkPicturePlayback out of SkPictureData

This splits the playback functionality out of SkPictureData. The old SkPictureData::draw method is pulled out along
with its supporting functions as verbatim as possible. Some follow on CLs will be required to:

   re-enable profiling in the debugger (and remove the vestiges of SkTimedPicture)
   re-enable display of command offsets in the picture (this should probably wait until we've switched to SkRecord though)
   Clean up CachedOperationList (maybe fuse with SkPicture::OperationList)
   Split SkPicturePlayback into a base class and two derived classes
   Implement parallel version of GatherGPUInfo for SkRecord

Landing this is blocked on removing Android's use of the abortPlayback entry point.

R=mtklein@google.com, reed@google.com

Author: robertphillips@google.com

Review URL: https://codereview.chromium.org/377623002
diff --git a/src/utils/SkPictureUtils.cpp b/src/utils/SkPictureUtils.cpp
index 702a78d..85d523f 100644
--- a/src/utils/SkPictureUtils.cpp
+++ b/src/utils/SkPictureUtils.cpp
@@ -190,7 +190,7 @@
     typedef SkBaseDevice INHERITED;
 };
 
-SkData* SkPictureUtils::GatherPixelRefs(SkPicture* pict, const SkRect& area) {
+SkData* SkPictureUtils::GatherPixelRefs(const SkPicture* pict, const SkRect& area) {
     if (NULL == pict) {
         return NULL;
     }