[printing] Improve Map printing

- Only show ElementsKind for JSObject Maps
- Display non-variable instance-size for non-JSObject Maps

Change-Id: I224b6ca2985f9c51635cc44ab5faa4cb977695ba
Reviewed-on: https://chromium-review.googlesource.com/946489
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51744}

src/objects-printer.cc

@@ -591,7 +591,12 @@ void Symbol::SymbolPrint(std::ostream& os) {  // NOLINT
 void Map::MapPrint(std::ostream& os) {  // NOLINT
   HeapObject::PrintHeader(os, "Map");
   os << "\n - type: " << instance_type();
-  os << "\n - instance size: " << instance_size();
+  os << "\n - instance size: ";
+  if (instance_size() == kVariableSizeSentinel) {
+    os << "variable";
+  } else {
+    os << instance_size();
+  }
   if (IsJSObjectMap()) {
     os << "\n - inobject properties: " << GetInObjectProperties();
   }

src/objects.cc

@@ -3246,10 +3246,16 @@ void HeapObject::HeapObjectShortPrint(std::ostream& os) {  // NOLINT
     return;
   }
   switch (map()->instance_type()) {
-    case MAP_TYPE:
-      os << "<Map(" << ElementsKindToString(Map::cast(this)->elements_kind())
-         << ")>";
-      break;
+    case MAP_TYPE: {
+      os << "<Map";
+      Map* mapInstance = Map::cast(this);
+      if (mapInstance->IsJSObjectMap()) {
+        os << "(" << ElementsKindToString(mapInstance->elements_kind()) << ")";
+      } else if (mapInstance->instance_size() != kVariableSizeSentinel) {
+        os << "[" << mapInstance->instance_size() << "]";
+      }
+      os << ">";
+    } break;
     case HASH_TABLE_TYPE:
       os << "<HashTable[" << FixedArray::cast(this)->length() << "]>";
       break;