Make SkCubicMap public

Bug: skia:8803
Change-Id: I3aa0814d538d95dc3a5a1034993b823d2151ab85
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/193961
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>

gn/core.gni

@@ -77,7 +77,6 @@ skia_core_sources = [
   "$_src/core/SkCubicClipper.cpp",
   "$_src/core/SkCubicClipper.h",
   "$_src/core/SkCubicMap.cpp",
-  "$_src/core/SkCubicMap.h",
   "$_src/core/SkData.cpp",
   "$_src/core/SkDataTable.cpp",
   "$_src/core/SkDebug.cpp",
@@ -365,6 +364,7 @@ skia_core_sources = [
   "$_include/core/SkColorSpaceXformCanvas.h",
   "$_include/core/SkContourMeasure.h",
   "$_include/core/SkCoverageMode.h",
+  "$_include/core/SkCubicMap.h",
   "$_include/core/SkData.h",
   "$_include/core/SkDataTable.h",
   "$_include/core/SkDeferredDisplayListRecorder.h",

include/core/SkCubicMap.h

@@ -18,7 +18,7 @@
  *  pt[3] is implicitly { 1, 1 }
  *  pts[1,2] are inside the unit square
  */
-class SkCubicMap {
+class SK_API SkCubicMap {
 public:
     SkCubicMap() {} // must call setPts() before using