Create stub GrAuditTrail class

include/private/GrAuditTrail.h

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef GrAuditTrail_DEFINED
+#define GrAuditTrail_DEFINED
+
+#include "SkString.h"
+#include "SkTArray.h"
+
+/*
+ * GrAuditTrail collects a list of draw ops, detailed information about those ops, and can dump them
+ * to json.
+ */
+class GrAuditTrail {
+public:
+    void addOp(SkString name) {
+        fOps.push_back().fName = name;
+    }
+
+    SkString toJson() const;
+
+    void reset() { fOps.reset(); }
+
+private:
+    struct Op {
+        SkString toJson() const;
+        SkString fName;
+    };
+
+    SkTArray<Op> fOps;
+};
+
+#endif