added initial GLSL support to skslc

src/sksl/ast/SkSLASTModifiers.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_ASTMODIFIERS
 #define SKSL_ASTMODIFIERS
 
 #include "SkSLASTLayout.h"
 #include "SkSLASTNode.h"
 
 namespace SkSL {
 
 /**
  * A set of modifier keywords (in, out, uniform, etc.) appearing before a declaration. 
  */
 struct ASTModifiers : public ASTNode {
     enum Flag {
-        kNo_Flag      =  0,
-        kConst_Flag   =  1,
-        kIn_Flag      =  2,
-        kOut_Flag     =  4,
-        kLowp_Flag    =  8,
-        kMediump_Flag = 16,
-        kHighp_Flag   = 32,
-        kUniform_Flag = 64
+        kNo_Flag            =  0,
+        kConst_Flag         =  1,
+        kIn_Flag            =  2,
+        kOut_Flag           =  4,
+        kLowp_Flag          =  8,
+        kMediump_Flag       = 16,
+        kHighp_Flag         = 32,
+        kUniform_Flag       = 64,
+        kFlat_Flag          = 128,
+        kNoPerspective_Flag = 256
     };
 
     ASTModifiers(ASTLayout layout, int flags)
     : fLayout(layout)
     , fFlags(flags) {}
 
     std::string description() const override {
         std::string result = fLayout.description();
         if (fFlags & kUniform_Flag) {
             result += "uniform ";
         }
         if (fFlags & kConst_Flag) {
             result += "const ";
         }
         if (fFlags & kLowp_Flag) {
             result += "lowp ";
         }
         if (fFlags & kMediump_Flag) {
             result += "mediump ";
         }
         if (fFlags & kHighp_Flag) {
             result += "highp ";
         }
+        if (fFlags & kFlat_Flag) {
+            result += "flat ";
+        }
+        if (fFlags & kNoPerspective_Flag) {
+            result += "noperspective ";
+        }
 
         if ((fFlags & kIn_Flag) && (fFlags & kOut_Flag)) {
             result += "inout ";
         } else if (fFlags & kIn_Flag) {
             result += "in ";
         } else if (fFlags & kOut_Flag) {
             result += "out ";
         }
 
         return result;
     }
 
     const ASTLayout fLayout;
     const int fFlags;
 };
 
 } // namespace
 
 #endif