Adding fast path for generalizing maps.

src/property-details.h

Index: src/property-details.h
diff --git a/src/property-details.h b/src/property-details.h
index dc912c8a0566a123eb11d0907eee5bd3f1e9ab0d..f025f152b7f02c46d641ba53f1b9f6a59d8336b0 100644
--- a/src/property-details.h
+++ b/src/property-details.h
@@ -99,16 +99,20 @@ class Representation {
 
   static Representation FromKind(Kind kind) { return Representation(kind); }
 
-  bool Equals(const Representation& other) {
+  bool Equals(const Representation& other) const {
     return kind_ == other.kind_;
   }
 
-  bool is_more_general_than(const Representation& other) {
+  bool is_more_general_than(const Representation& other) const {
     ASSERT(kind_ != kExternal);
     ASSERT(other.kind_ != kExternal);
     return kind_ > other.kind_;
   }
 
+  bool fits_into(const Representation& other) const {
+    return other.is_more_general_than(*this) || other.Equals(*this);
+  }
+
   Representation generalize(Representation other) {
     if (is_more_general_than(other)) {
       return *this;