add guard for fuchsia build

Bug: skia:
Change-Id: I3d4ae7c3dbae63001b2fab02d0f153390973f211
Reviewed-on: https://skia-review.googlesource.com/c/170345
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index ee55eaa..a2052c8 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -4,6 +4,7 @@
 # found in the LICENSE file.
 
 import("gn/flutter_defines.gni")
+import("gn/fuchsia_defines.gni")
 import("gn/shared_sources.gni")
 
 if (is_fuchsia) {
@@ -134,6 +135,9 @@
   if (skia_enable_atlas_text) {
     defines += [ "SK_SUPPORT_ATLAS_TEXT=1" ]
   }
+  if (is_fuchsia) {
+    defines += fuchsia_defines
+  }
 }
 
 # Skia internal APIs, used by Skia itself and a few test tools.