[sandbox] Disable the sandbox by default outside of Chromium builds

To work properly and securely, the sandbox requires cooperation from the
Embedder, for example in the form of a custom ArrayBufferAllocator and
later on custom type tags for external objects. As such, it likely does
not make sense to enable the sandbox by default everywhere.

Bug: v8:10391, v8:13058
Change-Id: Ief2720122f70b9a1bc3f2e6802e60b5b95b855d1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3771841Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Samuel Groß <saelo@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81805}

BUILD.gn

@@ -508,8 +508,9 @@ if (v8_enable_sandbox == "") {
   # once that is enabled everywhere by default.
   # TODO(chromium:1325784) the sandbox is not currently supported in Chromium
   # on Fuchsia.
-  v8_enable_sandbox = v8_enable_pointer_compression_shared_cage &&
-                      v8_enable_external_code_space && target_os != "fuchsia"
+  v8_enable_sandbox =
+      build_with_chromium && v8_enable_pointer_compression_shared_cage &&
+      v8_enable_external_code_space && target_os != "fuchsia"
 }
 
 # Enable sandboxed pointers when the sandbox is enabled.