Enable building angle_white_box_tests on Fuchsia

Builds fine.

Bug: angleproject:2475
Change-Id: I96b2b03e1be2b801c3d8579ebf44d51b6faa3e57
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2622235
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Yuly Novikov <ynovikov@chromium.org>

src/tests/BUILD.gn

@@ -221,7 +221,8 @@ if (is_win || is_linux || is_chromeos || is_mac || is_android || is_fuchsia ||
   }
 }
 
-if (is_win || is_linux || is_chromeos || is_mac || is_android || is_ios) {
+if (is_win || is_linux || is_chromeos || is_mac || is_android || is_fuchsia ||
+    is_ios) {
   import("angle_white_box_tests.gni")
 
   angle_test("angle_white_box_tests") {