clean up SkShader friends

Many SkShader subclasses are only friends to use makeColorSpace().

Our usual solution to this is to add a method on SkColorSpaceXformer
that calls makeColorSpace() for us, so that only SkColorSpaceXformer
needs to be a friend.

Just a refactor.  No image diffs.

Change-Id: Icf952b739edf45f2fb8c0c35e353ef2866f4c5cc
Reviewed-on: https://skia-review.googlesource.com/16370
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
diff --git a/src/core/SkColorSpaceXformer.h b/src/core/SkColorSpaceXformer.h
index 914e839..92d9260 100644
--- a/src/core/SkColorSpaceXformer.h
+++ b/src/core/SkColorSpaceXformer.h
@@ -16,11 +16,12 @@
 public:
     static std::unique_ptr<SkColorSpaceXformer> Make(sk_sp<SkColorSpace> dst);
 
-    sk_sp<SkImage> apply(const SkImage* src);
-    sk_sp<SkImage> apply(const SkBitmap& bitmap);
-    sk_sp<SkColorFilter> apply(const SkColorFilter* filter);
-    sk_sp<SkImageFilter> apply(const SkImageFilter* filter);
-    SkPaint apply(const SkPaint& src);
+    sk_sp<SkImage> apply(const SkImage*);
+    sk_sp<SkImage> apply(const SkBitmap&);
+    sk_sp<SkColorFilter> apply(const SkColorFilter*);
+    sk_sp<SkImageFilter> apply(const SkImageFilter*);
+    sk_sp<SkShader>      apply(const SkShader*);
+    SkPaint apply(const SkPaint&);
     void apply(SkColor dst[], const SkColor src[], int n);
     SkColor apply(SkColor srgb);