Turn on v8_enable_virtual_memory_cage for Chromium builds

This CL enables the virtual memory cage at compile time by default for
Chromium builds on x64 and arm64. However, the cage will only be used at
runtime if the correpsonding Chromium feature is enabled as well.

Bug: chromium:1218005
Change-Id: I5a452d299ac950f8ec0f741f6b9a153e57b2a666
Cq-Include-Trybots: luci.v8.try:v8_linux64_heap_sandbox_dbg_ng
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3200081Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Samuel Groß <saelo@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77212}

BUILD.gn

@@ -472,6 +472,13 @@ if (build_with_chromium && v8_current_cpu == "arm64" &&
   v8_control_flow_integrity = true
 }
 
+# Enable the virtual memory cage on 64-bit Chromium builds.
+if (build_with_chromium &&
+    (v8_current_cpu == "arm64" || v8_current_cpu == "x64")) {
+  # The cage is incompatible with lsan.
+  v8_enable_virtual_memory_cage = !is_lsan
+}
+
 assert(!v8_disable_write_barriers || v8_enable_single_generation,
        "Disabling write barriers works only with single generation")