Allow implicit conversion from GrSamplerState::Filter to GrSamplerState

constexprify GrSamplerState

pass/return GrSamplerState by value (it's 3 bytes).

Remove unused function from GrTexturePriv

Change-Id: Iffecd941500acf5653f01cc88b42ff1d45678b54
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/263346
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
diff --git a/src/gpu/gl/GrGLUniformHandler.cpp b/src/gpu/gl/GrGLUniformHandler.cpp
index f888473..d274166 100644
--- a/src/gpu/gl/GrGLUniformHandler.cpp
+++ b/src/gpu/gl/GrGLUniformHandler.cpp
@@ -60,7 +60,7 @@
 }
 
 GrGLSLUniformHandler::SamplerHandle GrGLUniformHandler::addSampler(const GrSurfaceProxy* texture,
-                                                                   const GrSamplerState&,
+                                                                   GrSamplerState,
                                                                    const GrSwizzle& swizzle,
                                                                    const char* name,
                                                                    const GrShaderCaps* shaderCaps) {