initial checkin of SkSL compiler

src/sksl/ir/SkSLExtension.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_EXTENSION
+#define SKSL_EXTENSION
+
+#include "SkSLProgramElement.h"
+
+namespace SkSL {
+
+/** 
+ * An extension declaration. 
+ */
+struct Extension : public ProgramElement {
+    Extension(Position position, std::string name)
+    : INHERITED(position, kExtension_Kind) 
+    , fName(std::move(name)) {}
+
+    std::string description() const override {
+        return "#extension " + fName + " : enable";
+    }
+
+    const std::string fName;
+
+    typedef ProgramElement INHERITED;
+};
+
+} // namespace
+
+#endif