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

gyp/core.gypi

 # Include this gypi to include all 'core' files
 # The parent gyp/gypi file must define
 #       'skia_src_path'     e.g. skia/trunk/src
 #       'skia_include_path' e.g. skia/trunk/include
 #
 # The skia build defines these in common_variables.gypi
 #
 {
     'sources': [
         '<(skia_src_path)/core/ARGB32_Clamp_Bilinear_BitmapShader.h',
@@ skipping 193 matching lines @@
 
         '<(skia_src_path)/doc/SkDocument.cpp',
 
         '<(skia_src_path)/image/SkImage.cpp',
         '<(skia_src_path)/image/SkImagePriv.cpp',
         '<(skia_src_path)/image/SkImage_Codec.cpp',
 #        '<(skia_src_path)/image/SkImage_Gpu.cpp',
         '<(skia_src_path)/image/SkImage_Picture.cpp',
         '<(skia_src_path)/image/SkImage_Raster.cpp',
         '<(skia_src_path)/image/SkSurface.cpp',
+        '<(skia_src_path)/image/SkSurface_Base.h',
 #        '<(skia_src_path)/image/SkSurface_Gpu.cpp',
         '<(skia_src_path)/image/SkSurface_Picture.cpp',
         '<(skia_src_path)/image/SkSurface_Raster.cpp',
 
         '<(skia_src_path)/pipe/SkGPipeRead.cpp',
         '<(skia_src_path)/pipe/SkGPipeWrite.cpp',
 
         '<(skia_include_path)/core/SkAdvancedTypefaceMetrics.h',
         '<(skia_include_path)/core/SkBitmap.h',
         '<(skia_include_path)/core/SkBitmapDevice.h',
@@ skipping 19 matching lines @@
         '<(skia_include_path)/core/SkEndian.h',
         '<(skia_include_path)/core/SkError.h',
         '<(skia_include_path)/core/SkFixed.h',
         '<(skia_include_path)/core/SkFlattenable.h',
         '<(skia_include_path)/core/SkFlattenableSerialization.h',
         '<(skia_include_path)/core/SkFloatBits.h',
         '<(skia_include_path)/core/SkFloatingPoint.h',
         '<(skia_include_path)/core/SkFontHost.h',
         '<(skia_include_path)/core/SkGeometry.h',
         '<(skia_include_path)/core/SkGraphics.h',
+        '<(skia_include_path)/core/SkImage.h',
         '<(skia_include_path)/core/SkImageDecoder.h',
         '<(skia_include_path)/core/SkImageEncoder.h',
         '<(skia_include_path)/core/SkImageFilter.h',
         '<(skia_include_path)/core/SkImageInfo.h',
         '<(skia_include_path)/core/SkInstCnt.h',
         '<(skia_include_path)/core/SkMallocPixelRef.h',
         '<(skia_include_path)/core/SkMask.h',
         '<(skia_include_path)/core/SkMaskFilter.h',
         '<(skia_include_path)/core/SkMath.h',
         '<(skia_include_path)/core/SkMatrix.h',
@@ skipping 15 matching lines @@
         '<(skia_include_path)/core/SkRect.h',
         '<(skia_include_path)/core/SkRefCnt.h',
         '<(skia_include_path)/core/SkRegion.h',
         '<(skia_include_path)/core/SkRRect.h',
         '<(skia_include_path)/core/SkScalar.h',
         '<(skia_include_path)/core/SkShader.h',
         '<(skia_include_path)/core/SkStream.h',
         '<(skia_include_path)/core/SkString.h',
         '<(skia_include_path)/core/SkStringUtils.h',
         '<(skia_include_path)/core/SkStrokeRec.h',
+        '<(skia_include_path)/core/SkSurface.h',
         '<(skia_include_path)/core/SkTArray.h',
         '<(skia_include_path)/core/SkTDArray.h',
         '<(skia_include_path)/core/SkTDStack.h',
         '<(skia_include_path)/core/SkTDict.h',
         '<(skia_include_path)/core/SkTInternalLList.h',
         '<(skia_include_path)/core/SkTileGridPicture.h',
         '<(skia_include_path)/core/SkTRegistry.h',
         '<(skia_include_path)/core/SkTSearch.h',
         '<(skia_include_path)/core/SkTemplates.h',
         '<(skia_include_path)/core/SkThread.h',
@@ skipping 62 matching lines @@
         '<(skia_src_path)/pathops/SkPathOpsPoint.h',
         '<(skia_src_path)/pathops/SkPathOpsQuad.h',
         '<(skia_src_path)/pathops/SkPathOpsRect.h',
         '<(skia_src_path)/pathops/SkPathOpsTriangle.h',
         '<(skia_src_path)/pathops/SkPathOpsTypes.h',
         '<(skia_src_path)/pathops/SkPathWriter.h',
         '<(skia_src_path)/pathops/SkQuarticRoot.h',
         '<(skia_src_path)/pathops/SkReduceOrder.h',
     ],
 }