[heap] Move and clarify TODO on RO_SPACE

Bug: v8:7464
Change-Id: I1b33bfff02ccd1ae19f0525e8ab0f8bfe69abe17
Reviewed-on: https://chromium-review.googlesource.com/c/1451933Reviewed-by: Dan Elphick <delphick@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Maciej Goszczycki <goszczycki@google.com>
Cr-Commit-Position: refs/heads/master@{#59348}

src/globals.h

@@ -650,7 +650,6 @@ typedef bool (*WeakSlotCallbackWithHeap)(Heap* heap, FullObjectSlot pointer);
 // NOTE: SpaceIterator depends on AllocationSpace enumeration values being
 // consecutive.
 enum AllocationSpace {
-  // TODO(v8:7464): Actually map this space's memory as read-only.
   RO_SPACE,    // Immortal, immovable and immutable objects,
   NEW_SPACE,   // Young generation semispaces for regular objects collected with
                // Scavenger.

src/heap/spaces.cc

@@ -3310,6 +3310,8 @@ void ReadOnlySpace::SetPermissionsForPages(PageAllocator::Permission access) {
     // page allocator manually.
     v8::PageAllocator* page_allocator =
         memory_allocator->page_allocator(page->executable());
+    // TODO(v8:7464): Map the whole space's memory read only (do not ignore the
+    // first page).
     CHECK(SetPermissions(page_allocator, page->address() + area_start_offset,
                          page->size() - area_start_offset, access));
   }