Add blend optimization helpers and use to convert rect draws to clears.

gyp/gpu.gypi

 # Include this gypi to include all 'gpu' 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
 #
 {
   'variables': {
     'skgpu_sources': [
@@ skipping 37 matching lines @@
       '<(skia_src_path)/gpu/GrAAConvexPathRenderer.cpp',
       '<(skia_src_path)/gpu/GrAAConvexPathRenderer.h',
       '<(skia_src_path)/gpu/GrAARectRenderer.cpp',
       '<(skia_src_path)/gpu/GrAddPathRenderers_default.cpp',
       '<(skia_src_path)/gpu/GrAllocator.h',
       '<(skia_src_path)/gpu/GrAllocPool.h',
       '<(skia_src_path)/gpu/GrAllocPool.cpp',
       '<(skia_src_path)/gpu/GrAtlas.cpp',
       '<(skia_src_path)/gpu/GrAtlas.h',
       '<(skia_src_path)/gpu/GrBinHashKey.h',
+      '<(skia_src_path)/gpu/GrBlend.cpp',
+      '<(skia_src_path)/gpu/GrBlend.h',
       '<(skia_src_path)/gpu/GrBufferAllocPool.cpp',
       '<(skia_src_path)/gpu/GrBufferAllocPool.h',
       '<(skia_src_path)/gpu/GrCacheID.cpp',
       '<(skia_src_path)/gpu/GrClipData.cpp',
       '<(skia_src_path)/gpu/GrContext.cpp',
       '<(skia_src_path)/gpu/GrDefaultPathRenderer.cpp',
       '<(skia_src_path)/gpu/GrDefaultPathRenderer.h',
       '<(skia_src_path)/gpu/GrDrawState.cpp',
       '<(skia_src_path)/gpu/GrDrawState.h',
       '<(skia_src_path)/gpu/GrDrawTarget.cpp',
@@ skipping 205 matching lines @@
       '<(skia_src_path)/gpu/gl/SkNullGLContext.cpp',
     ],
   },
 }
 
 # Local Variables:
 # tab-width:2
 # indent-tabs-mode:nil
 # End:
 # vim: set expandtab tabstop=2 shiftwidth=2: