added support for push_constant layout

src/sksl/ast/SkSLASTLayout.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_ASTLAYOUT
 #define SKSL_ASTLAYOUT
 
@@ skipping 62 matching lines @@
         } else if (str == "r8i") {
             *format = Format::kR8I;
             return true;
         }
         return false;
     }
 
     // For int parameters, a -1 means no value
     ASTLayout(int location, int binding, int index, int set, int builtin, int inputAttachmentIndex,
               bool originUpperLeft, bool overrideCoverage, bool blendSupportAllEquations,
-              Format format)
+              Format format, bool pushConstant)
     : fLocation(location)
     , fBinding(binding)
     , fIndex(index)
     , fSet(set)
     , fBuiltin(builtin)
     , fInputAttachmentIndex(inputAttachmentIndex)
     , fOriginUpperLeft(originUpperLeft)
     , fOverrideCoverage(overrideCoverage)
     , fBlendSupportAllEquations(blendSupportAllEquations)
-    , fFormat(format) {}
+    , fFormat(format)
+    , fPushConstant(pushConstant) {}
 
     SkString description() const {
         SkString result;
         SkString separator;
         if (fLocation >= 0) {
             result += separator + "location = " + to_string(fLocation);
             separator = ", ";
         }
         if (fBinding >= 0) {
             result += separator + "binding = " + to_string(fBinding);
@@ skipping 24 matching lines @@
             separator = ", ";
         }
         if (fBlendSupportAllEquations) {
             result += separator + "blend_support_all_equations";
             separator = ", ";
         }
         if (fFormat != Format::kUnspecified) {
             result += separator + FormatToStr(fFormat);
             separator = ", ";
         }
+        if (fPushConstant) {
+            result += separator + "push_constant";
+            separator = ", ";
+        }
         if (result.size() > 0) {
             result = "layout (" + result + ")";
         }
         return result;
     }
 
     const int fLocation;
     const int fBinding;
     const int fIndex;
     const int fSet;
     const int fBuiltin;
     const int fInputAttachmentIndex;
     const bool fOriginUpperLeft;
     const bool fOverrideCoverage;
     const bool fBlendSupportAllEquations;
     const Format fFormat;
+    const bool fPushConstant;
 };
 
 } // namespace
 
 #endif