Move SkRecordComputeLayers and CollectLayers into SkRecordDraw.cpp

Rather then exposing parts of FillBounds (as in Expose FillBounds to allow GrPictureUtils::CollectLayers to be layered on top of it - https://codereview.chromium.org/698643002/), this CL moves CollectLayers into SkRecordDraw.cpp to accomplish the layering.

Review URL: https://codereview.chromium.org/716913003
diff --git a/src/core/SkRecordDraw.h b/src/core/SkRecordDraw.h
index f3f0088..8df64cb 100644
--- a/src/core/SkRecordDraw.h
+++ b/src/core/SkRecordDraw.h
@@ -17,6 +17,13 @@
 // Fill a BBH to be used by SkRecordDraw to accelerate playback.
 void SkRecordFillBounds(const SkRect& cullRect, const SkRecord&, SkBBoxHierarchy*);
 
+#if SK_SUPPORT_GPU
+class GrAccelData;
+
+void SkRecordComputeLayers(const SkRect& cullRect, const SkRecord& record,
+                           SkBBoxHierarchy* bbh, GrAccelData* data);
+#endif
+
 // Draw an SkRecord into an SkCanvas.  A convenience wrapper around SkRecords::Draw.
 void SkRecordDraw(const SkRecord&, SkCanvas*, const SkBBoxHierarchy*, SkDrawPictureCallback*);