Remove support for GL discards

src/gpu/gl/GrGLGpu.h

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrGLGpu_DEFINED
 #define GrGLGpu_DEFINED
 
@@ skipping 36 matching lines @@
     GrGLStandard glStandard() const { return fGLContext->standard(); }
     GrGLVersion glVersion() const { return fGLContext->version(); }
     GrGLSLGeneration glslGeneration() const { return fGLContext->glslGeneration(); }
     const GrGLCaps& glCaps() const { return *fGLContext->caps(); }
 
     GrGLPathRendering* glPathRendering() {
         SkASSERT(glCaps().shaderCaps()->pathRenderingSupport());
         return static_cast<GrGLPathRendering*>(pathRendering());
     }
 
-    void discard(GrRenderTarget*);
-
     // Used by GrGLProgram to configure OpenGL state.
     void bindTexture(int unitIdx, const GrTextureParams& params, bool allowSRGBInputs,
                      GrGLTexture* texture);
 
     void bindTexelBuffer(int unitIdx, GrPixelConfig, GrGLBuffer*);
 
     void generateMipmaps(const GrTextureParams& params, bool allowSRGBInputs, GrGLTexture* texture);
 
     bool onGetReadPixelsInfo(GrSurface* srcSurface, int readWidth, int readHeight, size_t rowBytes,
                              GrPixelConfig readConfig, DrawPreference*,
@@ skipping 526 matching lines @@
     bool fHWPLSEnabled;
     bool fPLSHasBeenUsed;
 
     float fHWMinSampleShading;
 
     typedef GrGpu INHERITED;
     friend class GrGLPathRendering; // For accessing setTextureUnit.
 };
 
 #endif