Use glInvalidateFramebuffer() when it is supported.

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 57 matching lines @@
         kLast_MSFBOType = kES_EXT_MsToTexture_MSFBOType
     };
 
     enum FBFetchType {
         kNone_FBFetchType,
         /** GL_EXT_shader_framebuffer_fetch */
         kEXT_FBFetchType,
         /** GL_NV_shader_framebuffer_fetch */
         kNV_FBFetchType,
 
-        kLast_FBFetchType = kNV_FBFetchType,
+        kLast_FBFetchType = kNV_FBFetchType
+    };
+
+    enum InvalidateFBType {
+        kNone_InvalidateFBType,
+        kDiscard_InvalidateFBType,       //<! glDiscardFramebuffer()
+        kInvalidate_InvalidateFBType,     //<! glInvalidateFramebuffer()
+
+        kLast_InvalidateFBType = kInvalidate_InvalidateFBType
     };
 
     /**
      * Creates a GrGLCaps that advertises no support for any extensions,
      * formats, etc. Call init to initialize from a GrGLContextInfo.
      */
     GrGLCaps();
 
     GrGLCaps(const GrGLCaps& caps);
 
@@ skipping 63 matching lines @@
      * Is the MSAA FBO extension one where the texture is multisampled when bound to an FBO and
      * then implicitly resolved when read.
      */
     bool usesImplicitMSAAResolve() const {
         return kES_IMG_MsToTexture_MSFBOType == fMSFBOType ||
                kES_EXT_MsToTexture_MSFBOType == fMSFBOType;
     }
 
     FBFetchType fbFetchType() const { return fFBFetchType; }
 
+    InvalidateFBType invalidateFBType() const { return fInvalidateFBType; }
+
     /**
      * Returs a string containeng the caps info.
      */
     virtual SkString dump() const SK_OVERRIDE;
 
     /**
      * Gets an array of legal stencil formats. These formats are not guaranteed
      * to be supported by the driver but are legal GLenum names given the GL
      * version and extensions supported.
      */
@@ skipping 128 matching lines @@
     // tracks configs that have been verified to pass the FBO completeness when
     // used as a color attachment when a particular stencil format is used
     // as a stencil attachment.
     SkTArray<VerifiedColorConfigs, true> fStencilVerifiedColorConfigs;
 
     int fMaxFragmentUniformVectors;
     int fMaxVertexAttributes;
     int fMaxFragmentTextureUnits;
     int fMaxFixedFunctionTextureCoords;
 
-    MSFBOType fMSFBOType;
-
-    FBFetchType fFBFetchType;
+    MSFBOType           fMSFBOType;
+    FBFetchType         fFBFetchType;
+    InvalidateFBType    fInvalidateFBType;
 
     bool fRGBA8RenderbufferSupport : 1;
     bool fBGRAFormatSupport : 1;
     bool fBGRAIsInternalFormat : 1;
     bool fTextureSwizzleSupport : 1;
     bool fUnpackRowLengthSupport : 1;
     bool fUnpackFlipYSupport : 1;
     bool fPackRowLengthSupport : 1;
     bool fPackFlipYSupport : 1;
     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 fFullClearIsFree : 1;
     bool fDropsTileOnZeroDivide : 1;
 
     typedef GrDrawTargetCaps INHERITED;
 };
 
 #endif