[svg] Several filter helper tweaks

- Allow resolving inputs without modifying their colorspace
- Add helper to get the colorspace of a particular input
- Make resolveColorspace() virtual and add filter context to its
  signature

Bug: skia:10841
Change-Id: I2e226ec26205f527c2d171140072f106ec35fbe0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/356416
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Tyler Denniston <tdenniston@google.com>
diff --git a/modules/svg/src/SkSVGFeGaussianBlur.cpp b/modules/svg/src/SkSVGFeGaussianBlur.cpp
index 6ee1399..54ea011 100644
--- a/modules/svg/src/SkSVGFeGaussianBlur.cpp
+++ b/modules/svg/src/SkSVGFeGaussianBlur.cpp
@@ -29,9 +29,10 @@
         sigmaY *= objBounds.height();
     }
 
-    return SkImageFilters::Blur(sigmaX, sigmaY,
-                                fctx.resolveInput(ctx, this->getIn(), this->resolveColorspace(ctx)),
-                                this->resolveFilterSubregion(ctx, fctx));
+    return SkImageFilters::Blur(
+            sigmaX, sigmaY,
+            fctx.resolveInput(ctx, this->getIn(), this->resolveColorspace(ctx, fctx)),
+            this->resolveFilterSubregion(ctx, fctx));
 }
 
 template <>