added support for push_constant layout

src/sksl/ir/SkSLLayout.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_LAYOUT
 #define SKSL_LAYOUT
 
 namespace SkSL {
 
 /**
  * Represents a layout block appearing before a variable declaration, as in:
  *
  * layout (location = 0) int x;
  */
 struct Layout {
     Layout(const ASTLayout& layout)
     : fLocation(layout.fLocation)
     , fBinding(layout.fBinding)
     , fIndex(layout.fIndex)
     , fSet(layout.fSet)
     , fBuiltin(layout.fBuiltin)
     , fOriginUpperLeft(layout.fOriginUpperLeft)
     , fOverrideCoverage(layout.fOverrideCoverage)
-    , fBlendSupportAllEquations(layout.fBlendSupportAllEquations) {}
+    , fBlendSupportAllEquations(layout.fBlendSupportAllEquations)
+    , fPushConstant(layout.fPushConstant) {}
 
     Layout(int location, int binding, int index, int set, int builtin, bool originUpperLeft,
-           bool overrideCoverage, bool blendSupportAllEquations)
+           bool overrideCoverage, bool blendSupportAllEquations, bool pushconstant)
     : fLocation(location)
     , fBinding(binding)
     , fIndex(index)
     , fSet(set)
     , fBuiltin(builtin)
     , fOriginUpperLeft(originUpperLeft)
     , fOverrideCoverage(overrideCoverage)
-    , fBlendSupportAllEquations(blendSupportAllEquations) {}
+    , fBlendSupportAllEquations(blendSupportAllEquations)
+    , fPushConstant(pushconstant) {}
+
+    Layout() 
+    : fLocation(-1)
+    , fBinding(-1)
+    , fIndex(-1)
+    , fSet(-1)
+    , fBuiltin(-1)
+    , fOriginUpperLeft(false)
+    , fOverrideCoverage(false)
+    , fBlendSupportAllEquations(false)
+    , fPushConstant(false) {}
 
     std::string description() const {
         std::string result;
         std::string separator;
         if (fLocation >= 0) {
             result += separator + "location = " + to_string(fLocation);
             separator = ", ";
         }
         if (fBinding >= 0) {
             result += separator + "binding = " + to_string(fBinding);
@@ skipping 16 matching lines @@
             separator = ", ";
         }
         if (fOverrideCoverage) {
             result += separator + "override_coverage";
             separator = ", ";
         }
         if (fBlendSupportAllEquations) {
             result += separator + "blend_support_all_equations";
             separator = ", ";
         }
+        if (fPushConstant) {
+            result += separator + "push_constant";
+            separator = ", ";
+        }
         if (result.length() > 0) {
             result = "layout (" + result + ")";
         }
         return result;
     }
 
     bool operator==(const Layout& other) const {
         return fLocation                 == other.fLocation &&
                fBinding                  == other.fBinding &&
                fIndex                    == other.fIndex &&
                fSet                      == other.fSet &&
                fBuiltin                  == other.fBuiltin &&
                fOriginUpperLeft          == other.fOriginUpperLeft &&
                fOverrideCoverage         == other.fOverrideCoverage &&
                fBlendSupportAllEquations == other.fBlendSupportAllEquations;
     }
 
     bool operator!=(const Layout& other) const {
         return !(*this == other);
     }
 
-    // everything but builtin is in the GLSL spec; builtin comes from SPIR-V and identifies which
-    // particular builtin value this object represents.
     int fLocation;
     int fBinding;
     int fIndex;
     int fSet;
     int fBuiltin;
+    int fOffset;
     bool fOriginUpperLeft;
     bool fOverrideCoverage;
     bool fBlendSupportAllEquations;
+    bool fPushConstant;
 };
 
 } // namespace
 
 #endif