Rename SkSourceGammaTreatment to SkDestinationSurfaceColorMode

This is much more explicit about what that type represents (are we in
legacy mode or not), which also makes it suitable for other (upcoming)
usage.

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4529

Change-Id: Iacb397c34e7765f1ca86c0195bc622b2be4d9acf
Reviewed-on: https://skia-review.googlesource.com/4529
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
diff --git a/include/gpu/SkGr.h b/include/gpu/SkGr.h
index fc13c38..fae0c76 100644
--- a/include/gpu/SkGr.h
+++ b/include/gpu/SkGr.h
@@ -81,10 +81,10 @@
     texture is inserted into the cache (unless the bitmap is marked volatile) and can be
     retrieved again via this function. */
 GrTexture* GrRefCachedBitmapTexture(GrContext*, const SkBitmap&, const GrTextureParams&,
-                                    SkSourceGammaTreatment);
+                                    SkDestinationSurfaceColorMode);
 
 sk_sp<GrTexture> GrMakeCachedBitmapTexture(GrContext*, const SkBitmap&, const GrTextureParams&,
-                                           SkSourceGammaTreatment);
+                                           SkDestinationSurfaceColorMode);
 
 // TODO: Move SkImageInfo2GrPixelConfig to SkGrPriv.h (requires cleanup to SkWindow its subclasses).
 GrPixelConfig SkImageInfo2GrPixelConfig(SkColorType, SkAlphaType, const SkColorSpace*,