move a bunch of helpers from SkImageInfo.h into priv

Bug: skia:
Change-Id: I8c91cfdb89e4f22448d1201d391556fe43d86dca
Reviewed-on: https://skia-review.googlesource.com/105289
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
Reviewed-by: Cary Clark <caryclark@google.com>
diff --git a/src/codec/SkWebpCodec.cpp b/src/codec/SkWebpCodec.cpp
index 6618072..95ae9b9 100644
--- a/src/codec/SkWebpCodec.cpp
+++ b/src/codec/SkWebpCodec.cpp
@@ -617,7 +617,7 @@
     const bool needsSrgbToLinear = dstInfo.gammaCloseToSRGB() &&
             options.fPremulBehavior == SkTransferFunctionBehavior::kRespect;
 
-    const size_t dstBpp = SkColorTypeBytesPerPixel(dstInfo.colorType());
+    const size_t dstBpp = dstInfo.bytesPerPixel();
     dst = SkTAddOffset<void>(dst, dstBpp * dstX + rowBytes * dstY);
     const size_t srcRowBytes = config.output.u.RGBA.stride;