Make GrRenderableConfigForColorSpace argument const

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2367813002

Review-Url: https://codereview.chromium.org/2367813002
diff --git a/src/gpu/SkGr.cpp b/src/gpu/SkGr.cpp
index 9ee8722..6d1e735 100644
--- a/src/gpu/SkGr.cpp
+++ b/src/gpu/SkGr.cpp
@@ -508,7 +508,7 @@
     return true;
 }
 
-GrPixelConfig GrRenderableConfigForColorSpace(SkColorSpace* colorSpace) {
+GrPixelConfig GrRenderableConfigForColorSpace(const SkColorSpace* colorSpace) {
     if (!colorSpace) {
         return kRGBA_8888_GrPixelConfig;
     } else if (colorSpace->gammaIsLinear()) {
diff --git a/src/gpu/SkGrPriv.h b/src/gpu/SkGrPriv.h
index c1069d1..b658389 100644
--- a/src/gpu/SkGrPriv.h
+++ b/src/gpu/SkGrPriv.h
@@ -108,7 +108,7 @@
 /** When image filter code needs to construct a draw context to do intermediate rendering, we need
     a renderable pixel config. The source (SkSpecialImage) may not be in a renderable format, but
     we want to preserve the color space of that source. This picks an appropriate format to use. */
-GrPixelConfig GrRenderableConfigForColorSpace(SkColorSpace*);
+GrPixelConfig GrRenderableConfigForColorSpace(const SkColorSpace*);
 
 /**
  *  If the compressed data in the SkData is supported (as a texture format, this returns