GN: Reset default for fallback root certs to false.

runtime/bin/BUILD.gn

 # Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 import("gypi_contents.gni")
 
 declare_args() {
   # Whether to fall back to built-in root certificates when they cannot be
   # verified at the operating system level.
-  dart_use_fallback_root_certificates = true
+  dart_use_fallback_root_certificates = false
 
   # The BUILD.gn file that we pull from chromium as part of zlib has a
   # dependence on //base, which we don't pull in. In a standalone build of the
   # VM, we set this to //runtime/bin/zlib where we have a BUILD.gn file without
   # a dependence on //base.
   dart_zlib_path = "//third_party/zlib"
 
   # Whether to link the standalone VM against tcmalloc. The standalone build of
   # the VM enables this only for Linux builds.
   dart_use_tcmalloc = false
 }
 
+# TODO(zra): Remove this when Fuchsia has a root cert cache on the filesystem.
+if (defined(is_fuchsia) && is_fuchsia) {
+  dart_use_fallback_root_certificates = true
+}
+
 # Generate a resources.cc file for the service isolate without Observatory.
 action("gen_resources_cc") {
   visibility = [ ":*" ]  # Only targets in this file can see this.
   script = "../tools/create_resources.py"
   inputs = [
     "../tools/create_resources.py",
   ]
 
   # The path below is hard coded for the Mojo and Flutter trees. When moving
   # the Dart runtime to gn, this path might need to be updated.
@@ skipping 806 matching lines @@
       # The only effect of DART_SHARED_LIB is to export the Dart API.
       "DART_SHARED_LIB",
     ]
     if (is_win) {
       libs = [ "dart.lib" ]
       abs_root_out_dir = rebase_path(root_out_dir)
       ldflags = [ "/LIBPATH:$abs_root_out_dir" ]
     }
   }
 }