Add Audittrail for path renderers

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1588683002

Review URL: https://codereview.chromium.org/1588683002
diff --git a/src/gpu/GrDrawTarget.h b/src/gpu/GrDrawTarget.h
index d16d6e8..55c11da 100644
--- a/src/gpu/GrDrawTarget.h
+++ b/src/gpu/GrDrawTarget.h
@@ -167,6 +167,8 @@
 
     const CMMAccess cmmAccess() { return CMMAccess(this); }
 
+    GrAuditTrail* getAuditTrail() const { return fAuditTrail; }
+
 private:
     friend class GrDrawingManager; // for resetFlag & TopoSortTraits