Create optimized versions of the Map/Set clear method

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index cc93bde592a5d7151821892bb084ee5b280f1e44..67184ff06b063b8be8250580231df5b3d8ae230a 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -3921,6 +3921,7 @@ class OrderedHashTable: public FixedArray {
   static const int kNumberOfElementsIndex = kNumberOfBucketsIndex + 1;
   static const int kNumberOfDeletedElementsIndex = kNumberOfElementsIndex + 1;
   static const int kHashTableStartIndex = kNumberOfDeletedElementsIndex + 1;
+  static const int kNextTableIndex = kNumberOfElementsIndex;
 
   static const int kNumberOfBucketsOffset =
       kHeaderSize + kNumberOfBucketsIndex * kPointerSize;
@@ -3930,12 +3931,19 @@ class OrderedHashTable: public FixedArray {
       kHeaderSize + kNumberOfDeletedElementsIndex * kPointerSize;
   static const int kHashTableStartOffset =
       kHeaderSize + kHashTableStartIndex * kPointerSize;
+  static const int kNextTableOffset =
+      kHeaderSize + kNextTableIndex * kPointerSize;
 
   static const int kEntrySize = entrysize + 1;
   static const int kChainOffset = entrysize;
 
   static const int kLoadFactor = 2;
 
+  // NumberOfDeletedElements is set to kClearedTableSentinel when
+  // the table is cleared, which allows iterator transitions to
+  // optimize that case.
+  static const int kClearedTableSentinel = -1;
+
  private:
   static Handle<Derived> Rehash(Handle<Derived> table, int new_capacity);
 
@@ -3977,7 +3985,6 @@ class OrderedHashTable: public FixedArray {
     return set(kRemovedHolesIndex + index, Smi::FromInt(removed_index));
   }
 
-  static const int kNextTableIndex = kNumberOfElementsIndex;
   static const int kRemovedHolesIndex = kHashTableStartIndex;
 
   static const int kMaxCapacity =