Add iOS support for SkiaSDLExample.

Change-Id: Ib8f4d6c41356cf0fe2e14b7bff7713d107eaa01f
Reviewed-on: https://skia-review.googlesource.com/40687
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index a080e93..98bfdc5 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -1640,7 +1640,7 @@
     }
   }
 
-  if (skia_enable_gpu && (is_linux || is_mac)) {
+  if (skia_enable_gpu && (is_linux || is_mac || is_ios)) {
     test_app("SkiaSDLExample") {
       sources = [
         "example/SkiaSDLExample.cpp",