Remove GetHeaps from String::MakeExternal by first checking the String
is not in RO_SPACE (by checking the MemoryChunk's identity) and only
then getting the heap from the chunk. Also changes
String::CanMakeExternal in api.cc to not use GetHeap.

Also remove check GetHeap()->Contains(this/map) that attempts to print
INVALID POINTER/INVALID MAP as it's much more likely that the code will
crash in either GetHeap or Contains before printing anything.

Bug: v8:7786
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: Id27ba84eb2ba78c71158d6f2e94a3b4176c34609
Reviewed-on: https://chromium-review.googlesource.com/1131128
Commit-Queue: Dan Elphick <delphick@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54361}