Don’t build benchmarking binaries on Windows. (#6428)

BUILD.gn

@@ -38,12 +38,15 @@ group("flutter") {
       "$flutter_root/flow:flow_unittests",
       "$flutter_root/fml:fml_unittests",
       "$flutter_root/runtime:runtime_unittests",
-      "$flutter_root/shell/common:shell_benchmarks",
       "$flutter_root/shell/common:shell_unittests",
       "$flutter_root/shell/platform/embedder:embedder_unittests",
       "$flutter_root/synchronization:synchronization_unittests",
       "$flutter_root/third_party/txt:txt_unittests",
     ]
+
+    if (!is_win) {
+      public_deps += [ "$flutter_root/shell/common:shell_benchmarks" ]
+    }
   }
 }