added basic dataflow analysis to skslc

src/sksl/ir/SkSLExpression.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_EXPRESSION
 #define SKSL_EXPRESSION
 
@@ skipping 15 matching lines @@
         kFloatLiteral_Kind,
         kFunctionReference_Kind,
         kFunctionCall_Kind,
         kIndex_Kind,
         kPrefix_Kind,
         kPostfix_Kind,
         kSwizzle_Kind,
         kVariableReference_Kind,
         kTernary_Kind,
         kTypeReference_Kind,
+        kDefined_Kind
     };
 
     Expression(Position position, Kind kind, const Type& type)
     : INHERITED(position)
     , fKind(kind)
     , fType(std::move(type)) {}
 
     virtual bool isConstant() const {
         return false;
     }
 
     const Kind fKind;
     const Type& fType;
 
     typedef IRNode INHERITED;
 };
 
 } // namespace
 
 #endif