Revert "Revert "Add Atlas Text interface for rendering SDF glyphs.""

This reverts commit 9c2202ffc22b4293b48a4edeafa1b5d2bab8bb83.

Bug: skia:
Change-Id: I482ddf74f8e40d3d0908c840ba5c6ff981ccefbd
Reviewed-on: https://skia-review.googlesource.com/73345
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
diff --git a/gn/gm.gni b/gn/gm.gni
index 441c041..22d562f 100644
--- a/gn/gm.gni
+++ b/gn/gm.gni
@@ -22,6 +22,7 @@
   "$_gm/arcofzorro.cpp",
   "$_gm/arcto.cpp",
   "$_gm/arithmode.cpp",
+  "$_gm/atlastext.cpp",
   "$_gm/badpaint.cpp",
   "$_gm/beziereffects.cpp",
   "$_gm/beziers.cpp",