Add discard API to SkCanvas, plumb it to glDiscardFramebuffer()

src/gpu/gl/GrGLCaps.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #ifndef GrGLCaps_DEFINED
 #define GrGLCaps_DEFINED
@@ skipping 227 matching lines @@
 
     /// Does ReadPixels support the provided format/type combo?
     bool readPixelsSupported(const GrGLInterface* intf,
                              GrGLenum format,
                              GrGLenum type) const;
 
     bool isCoreProfile() const { return fIsCoreProfile; }
 
     bool fixedFunctionSupport() const { return fFixedFunctionSupport; }
 
-    /// Is there support for discarding the frame buffer
-    bool discardFBSupport() const { return fDiscardFBSupport; }
-
     bool fullClearIsFree() const { return fFullClearIsFree; }
 
 private:
     /**
      * Maintains a bit per GrPixelConfig. It is used to avoid redundantly
      * performing glCheckFrameBufferStatus for the same config.
      */
     struct VerifiedColorConfigs {
         VerifiedColorConfigs() {
             this->reset();
@@ skipping 62 matching lines @@
     bool fTextureUsageSupport : 1;
     bool fTexStorageSupport : 1;
     bool fTextureRedSupport : 1;
     bool fImagingSupport  : 1;
     bool fTwoFormatLimit : 1;
     bool fFragCoordsConventionSupport : 1;
     bool fVertexArrayObjectSupport : 1;
     bool fUseNonVBOVertexAndIndexDynamicData : 1;
     bool fIsCoreProfile : 1;
     bool fFixedFunctionSupport : 1;
-    bool fDiscardFBSupport : 1;
     bool fFullClearIsFree : 1;
 
     typedef GrDrawTargetCaps INHERITED;
 };
 
 #endif