initial checkin of SkSL compiler

src/sksl/ir/SkSLIRNode.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 SKSL_IRNODE
+#define SKSL_IRNODE
+
+#include "../SkSLPosition.h"
+
+namespace SkSL {
+
+/**
+ * Represents a node in the intermediate representation (IR) tree. The IR is a fully-resolved 
+ * version of the program (all types determined, everything validated), ready for code generation.
+ */
+struct IRNode {
+    IRNode(Position position)
+    : fPosition(position) {}
+
+    virtual ~IRNode() {}
+
+    virtual std::string description() const = 0;
+
+    const Position fPosition;
+};
+
+} // namespace
+
+#endif