Revert of Turned on SkSL->GLSL compiler

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 17 matching lines @@
 struct ASTDiscardStatement;
 struct ASTDoStatement;
 struct ASTExpression;
 struct ASTExpressionStatement;
 struct ASTForStatement;
 struct ASTIfStatement;
 struct ASTInterfaceBlock;
 struct ASTLayout;
 struct ASTModifiers;
 struct ASTParameter;
-struct ASTPrecision;
 struct ASTReturnStatement;
 struct ASTStatement;
 struct ASTSuffix;
 struct ASTType;
 struct ASTWhileStatement;
 struct ASTVarDeclarations;
 class SymbolTable;
 
 /**
  * Consumes .sksl text and produces an abstract syntax tree describing the contents.
@@ skipping 45 matching lines @@
     /**
      * Returns true if the 'name' identifier refers to a type name. For instance, isType("int") will
      * always return true.
      */
     bool isType(std::string name);
 
     // these functions parse individual grammar rules from the current parse position; you probably
     // don't need to call any of these outside of the parser. The function declarations in the .cpp
     // file have comments describing the grammar rules.
 
-    std::unique_ptr<ASTDeclaration> precision();
+    void precision();
 
     std::unique_ptr<ASTDeclaration> directive();
 
     std::unique_ptr<ASTDeclaration> declaration();
 
     std::unique_ptr<ASTVarDeclarations> varDeclarations();
 
     std::unique_ptr<ASTType> structDeclaration();
 
     std::unique_ptr<ASTVarDeclarations> structVarDeclaration(ASTModifiers modifiers);
@@ skipping 86 matching lines @@
     void* fScanner;
     YY_BUFFER_STATE fBuffer;
     Token fPushback;
     SymbolTable& fTypes;
     ErrorReporter& fErrors;
 };
 
 } // namespace
 
 #endif