sk_tools/Resources: optional SK_TOOLS_REQUIRE_RESOURCES flag

BUG=skia:7842
Change-Id: I1ce7d12308cd8ee101163d73dfc79f2d2155c632
Reviewed-on: https://skia-review.googlesource.com/123425
Auto-Submit: Hal Canary <halcanary@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
Reviewed-by: Florin Malita <fmalita@chromium.org>
diff --git a/BUILD.gn b/BUILD.gn
index 3eb5c54..1ebd6e6 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -54,6 +54,8 @@
 
   skia_llvm_path = ""
   skia_llvm_lib = "LLVM"
+
+  skia_tools_require_resources = false
 }
 declare_args() {
   skia_use_dng_sdk = !is_fuchsia && skia_use_libjpeg_turbo && skia_use_zlib
@@ -1344,6 +1346,10 @@
       sources += [ "tools/ios_utils.m" ]
       libs += [ "Foundation.framework" ]
     }
+    defines = []
+    if (skia_tools_require_resources) {
+      defines += [ "SK_TOOLS_REQUIRE_RESOURCES" ]
+    }
     deps = [
       ":common_flags",
       ":experimental_svg_model",