Stop discarding in frag shader when coverage is zero and stencil writes are enabled

src/gpu/gl/GrGLProgramDesc.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrGLProgramDesc_DEFINED
 #define GrGLProgramDesc_DEFINED
 
@@ skipping 133 matching lines @@
     }
 
     struct KeyHeader {
         GrGLShaderBuilder::DstReadKey fDstReadKey;      // set by GrGLShaderBuilder if there
                                                         // are effects that must read the dst.
                                                         // Otherwise, 0.
         GrGLShaderBuilder::FragPosKey fFragPosKey;      // set by GrGLShaderBuilder if there are
                                                         // effects that read the fragment position.
                                                         // Otherwise, 0.
 
-        // should the FS discard if the coverage is zero (to avoid stencil manipulation)
-        SkBool8                     fDiscardIfZeroCoverage;
-
         ColorInput                  fColorInput : 8;
         ColorInput                  fCoverageInput : 8;
         CoverageOutput              fCoverageOutput : 8;
 
         SkBool8                     fHasVertexCode;
         SkBool8                     fEmitsPointSize;
 
         // To enable experimental geometry shader code (not for use in
         // production)
 #if GR_GL_EXPERIMENTAL_GS
@@ skipping 51 matching lines @@
 
     // GrGLProgram and GrGLShaderBuilder read the private fields to generate code. TODO: Move all
     // code generation to GrGLShaderBuilder (and maybe add getters rather than friending).
     friend class GrGLProgram;
     friend class GrGLShaderBuilder;
     friend class GrGLFullShaderBuilder;
     friend class GrGLFragmentOnlyShaderBuilder;
 };
 
 #endif