Move SkOSFile.h to src/core

Skia needs implementations (ports) of the declarations in this header,
but no one outside of Skia the library should use them.

Change-Id: I1b92eca787a61892d7b3c0ac8c5996774429ae24
Reviewed-on: https://skia-review.googlesource.com/9878
Commit-Queue: Ben Wagner <bungeman@google.com>
Reviewed-by: Mike Reed <reed@google.com>
Reviewed-by: Leon Scroggins <scroggo@google.com>
diff --git a/gn/core.gni b/gn/core.gni
index db5cd6c..3e2e53e 100644
--- a/gn/core.gni
+++ b/gn/core.gni
@@ -221,6 +221,7 @@
   "$_src/core/SkOpts.cpp",
   "$_src/core/SkOpts.h",
   "$_src/core/SkOrderedReadBuffer.h",
+  "$_src/core/SkOSFile.h",
   "$_src/core/SkOverdrawCanvas.cpp",
   "$_src/core/SkOverdrawCanvas.h",
   "$_src/core/SkPaint.cpp",
@@ -416,7 +417,6 @@
   "$_include/core/SkMatrix44.h",
   "$_include/core/SkMetaData.h",
   "$_include/core/SkMultiPictureDraw.h",
-  "$_include/core/SkOSFile.h",
   "$_include/core/SkPaint.h",
   "$_include/core/SkPath.h",
   "$_include/core/SkPathEffect.h",
diff --git a/include/core/SkOSFile.h b/src/core/SkOSFile.h
similarity index 100%
rename from include/core/SkOSFile.h
rename to src/core/SkOSFile.h