[Fuchsia] Always call zx_vmo_replace_as_executable() in OS::Allocate()

OS::Allocate() previously was calling zx_vmo_replace_as_executable()
when executable access is requested. This breaks the case when the
OS::SetPermission() is called to mark that memory as executable later.
Updated it to call zx_vmo_replace_as_executable() for all VMOs.

This solution is not ideal, but it's consistent with other platforms,
so it's acceptable short-term.

Bug: v8:8899, chromium:934582
Change-Id: Ifeb818c93d8b9c80e73a057f5e6f3ca5a7b1c23f
Reviewed-on: https://chromium-review.googlesource.com/c/1483613Reviewed-by: Wez <wez@chromium.org>
Commit-Queue: Sergey Ulanov <sergeyu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59880}

src/base/platform/platform-fuchsia.cc

@@ -54,13 +54,17 @@ void* OS::Allocate(void* address, size_t size, size_t alignment,
   static const char kVirtualMemoryName[] = "v8-virtualmem";
   zx_object_set_property(vmo, ZX_PROP_NAME, kVirtualMemoryName,
                          strlen(kVirtualMemoryName));
+
+  // Always call zx_vmo_replace_as_executable() in case the memory will need
+  // to be marked as executable in the future.
+  // TOOD(https://crbug.com/v8/8899): Only call this when we know that the
+  // region will need to be marked as executable in the future.
+  if (zx_vmo_replace_as_executable(vmo, ZX_HANDLE_INVALID, &vmo) != ZX_OK) {
+    return nullptr;
+  }
+
   uintptr_t reservation;
   uint32_t prot = GetProtectionFromMemoryPermission(access);
-  if ((prot & ZX_VM_PERM_EXECUTE) != 0) {
-    if (zx_vmo_replace_as_executable(vmo, ZX_HANDLE_INVALID, &vmo) != ZX_OK) {
-      return nullptr;
-    }
-  }
   zx_status_t status = zx_vmar_map(zx_vmar_root_self(), prot, 0, vmo, 0,
                                    request_size, &reservation);
   // Either the vmo is now referenced by the vmar, or we failed and are bailing,