move SkDraw.h to core

BUG=skia:

Change-Id: Ic8c949530414f3f8d7caded969941dc853a06271
Reviewed-on: https://skia-review.googlesource.com/6845
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>

gn/core.gni

@@ -112,6 +112,7 @@ skia_core_sources = [
   "$_src/core/SkDither.h",
   "$_src/core/SkDocument.cpp",
   "$_src/core/SkDraw.cpp",
+  "$_src/core/SkDraw.h",
   "$_src/core/SkDrawable.cpp",
   "$_src/core/SkDrawLooper.cpp",
   "$_src/core/SkDrawProcs.h",
@@ -389,7 +390,6 @@ skia_core_sources = [
   "$_include/core/SkData.h",
   "$_include/core/SkDeque.h",
   "$_include/core/SkDevice.h",
-  "$_include/core/SkDraw.h",
   "$_include/core/SkDrawable.h",
   "$_include/core/SkDrawFilter.h",
   "$_include/core/SkDrawLooper.h",