[ubsan] Fix Map::PrintMapDetails.

Now that Map just contains a pointer, and is passed by value to
Logger::MapDetails, printing the this pointer in Map::PrintMapDetails no longer
makes sense, but we need to print the underlying pointer.

BUG=v8:3770

Change-Id: I87f41c796dbff7a8800731bb1d63a7482b9ff71c
Reviewed-on: https://chromium-review.googlesource.com/c/1347485
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57733}

src/objects-printer.cc

@@ -2400,7 +2400,7 @@ void Map::PrintMapDetails(std::ostream& os) {
 #ifdef OBJECT_PRINT
   this->MapPrint(os);
 #else
-  os << "Map=" << reinterpret_cast<void*>(this);
+  os << "Map=" << reinterpret_cast<void*>(ptr());
 #endif
   os << "\n";
   instance_descriptors()->PrintDescriptors(os);