Fix issue with -0 in Maps

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 100cbf90b3493860d8bd0c5c5b4246d8f57e495d..99b0ab70de998065185c0d504ba487f31b6a08a7 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -798,10 +798,16 @@ Map* Object::GetRootMap(Isolate* isolate) {
 Object* Object::GetHash() {
   // The object is either a number, a name, an odd-ball,
   // a real JS object, or a Harmony proxy.
-  if (IsNumber()) {
-    uint32_t hash = std::isnan(Number())
-                        ? Smi::kMaxValue
-                        : ComputeLongHash(double_to_uint64(Number()));
+  if (IsSmi()) {
+    int num = Smi::cast(this)->value();
+    uint32_t hash = ComputeLongHash(double_to_uint64(static_cast<double>(num)));
+    return Smi::FromInt(hash & Smi::kMaxValue);
+  }
+  if (IsHeapNumber()) {
+    double num = HeapNumber::cast(this)->value();
+    if (std::isnan(num)) return Smi::FromInt(Smi::kMaxValue);
+    if (i::IsMinusZero(num)) num = 0;
+    uint32_t hash = ComputeLongHash(double_to_uint64(num));
     return Smi::FromInt(hash & Smi::kMaxValue);
   }
   if (IsName()) {