Start to propagate constness of GrPipelineBuilder up the stack

src/gpu/gl/GrGLGpu.cpp

Index: src/gpu/gl/GrGLGpu.cpp
diff --git a/src/gpu/gl/GrGLGpu.cpp b/src/gpu/gl/GrGLGpu.cpp
index e185ef01a56c11e760b07006c82ef8748b188e4a..7320d2e30eeeb0b8d1bf04aa1e930547977ca2e5 100644
--- a/src/gpu/gl/GrGLGpu.cpp
+++ b/src/gpu/gl/GrGLGpu.cpp
@@ -2676,7 +2676,7 @@ void GrGLGpu::unbindTextureFromFBO(GrGLenum fboTarget) {
                                                          0));
 }
 
-bool GrGLGpu::initCopySurfaceDstDesc(const GrSurface* src, GrSurfaceDesc* desc) {
+bool GrGLGpu::initCopySurfaceDstDesc(const GrSurface* src, GrSurfaceDesc* desc) const {
     // If the src is a texture, we can implement the blit as a draw assuming the config is
     // renderable.
     if (src->asTexture() && this->caps()->isConfigRenderable(src->config(), false)) {