Added skslc parse recursion limit

src/sksl/SkSLParser.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_PARSER
 #define SKSL_PARSER
 
@@ skipping 179 matching lines @@
     std::unique_ptr<ASTExpression> term();
 
     bool intLiteral(int64_t* dest);
 
     bool floatLiteral(double* dest);
 
     bool boolLiteral(bool* dest);
 
     bool identifier(std::string* dest);
 
-
     void* fScanner;
     YY_BUFFER_STATE fBuffer;
+    // current parse depth, used to enforce a recursion limit to try to keep us from overflowing the
+    // stack on pathological inputs
+    int fDepth = 0;
     Token fPushback;
     SymbolTable& fTypes;
     ErrorReporter& fErrors;
+
+    friend class AutoDepth;
 };
 
 } // namespace
 
 #endif