Add a private API for writing the clip to the stencil

Add a private API used by Android framework, which writes the clip
into a stencil buffer. This is used by HWUI to clip the WebView.

Bug: 31489986
Change-Id: I94515f1539acd9d069c8aceb3300577feed9c94f
Reviewed-on: https://skia-review.googlesource.com/29521
Commit-Queue: Stan Iliev <stani@google.com>
Reviewed-by: Derek Sollenberger <djsollen@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index d837d1d..08b94cd 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -678,6 +678,7 @@
   sources += skia_utils_sources
   sources += skia_xps_sources
   sources += [
+    "src/android/SkAndroidFrameworkUtils.cpp",
     "src/android/SkBitmapRegionCodec.cpp",
     "src/android/SkBitmapRegionDecoder.cpp",
     "src/codec/SkAndroidCodec.cpp",