Make BBH parameter to SkRecordComputeLayers and SkRecordFillBounds optional

src/core/SkRecordDraw.cpp

Index: src/core/SkRecordDraw.cpp
diff --git a/src/core/SkRecordDraw.cpp b/src/core/SkRecordDraw.cpp
index e35e5a0a9d37d37e5c232067108a20680d03c511..77235fda415577eb1c6288c8de87cdd9d91a4492 100644
--- a/src/core/SkRecordDraw.cpp
+++ b/src/core/SkRecordDraw.cpp
@@ -168,8 +168,9 @@ public:
         }
 
         // Finally feed all stored bounds into the BBH.  They'll be returned in this order.
-        SkASSERT(bbh);
-        bbh->insert(&fBounds, fNumRecords);
+        if (bbh) {
+            bbh->insert(&fBounds, fNumRecords);
+        }
     }
 
     template <typename T> void operator()(const T& op) {