make alpha read back of bgra/rgba work

src/gpu/gl/GrGLGpu.h

Index: src/gpu/gl/GrGLGpu.h
diff --git a/src/gpu/gl/GrGLGpu.h b/src/gpu/gl/GrGLGpu.h
index d802f08b75b236ce6a8820a82e50b7a565fbd97d..20dcafa9154f55fe008a8e992e2717a7ebb03aa3 100644
--- a/src/gpu/gl/GrGLGpu.h
+++ b/src/gpu/gl/GrGLGpu.h
@@ -194,8 +194,7 @@ private:
                        const GrNonInstancedVertices& vertices,
                        size_t* indexOffsetInBytes);
 
-    // Subclasses should call this to flush the blend state.
-    void flushBlend(const GrXferProcessor::BlendInfo& blendInfo);
+    void flushBlend(const GrXferProcessor::BlendInfo& blendInfo, bool swapConstRedAndAlpha);
 
     bool hasExtension(const char* ext) const { return fGLContext->hasExtension(ext); }