Free one bit in Map by removing unused retaining counter.

src/mips/builtins-mips.cc

Index: src/mips/builtins-mips.cc
diff --git a/src/mips/builtins-mips.cc b/src/mips/builtins-mips.cc
index a617ff8f21a026820f0d0793798bf970a5b91cba..9167c70c0c7f4b86e5d6ee0ebcdd873018a6f0e1 100644
--- a/src/mips/builtins-mips.cc
+++ b/src/mips/builtins-mips.cc
@@ -423,12 +423,12 @@ static void Generate_JSConstructStubHelper(MacroAssembler* masm,
           MemOperand bit_field3 = FieldMemOperand(a2, Map::kBitField3Offset);
           // Check if slack tracking is enabled.
           __ lw(t0, bit_field3);
-          __ DecodeField<Map::Counter>(t2, t0);
+          __ DecodeField<Map::ConstructionCounter>(t2, t0);
           // t2: slack tracking counter
           __ Branch(&no_inobject_slack_tracking, lt, t2,
                     Operand(Map::kSlackTrackingCounterEnd));
           // Decrease generous allocation count.
-          __ Subu(t0, t0, Operand(1 << Map::Counter::kShift));
+          __ Subu(t0, t0, Operand(1 << Map::ConstructionCounter::kShift));
           __ sw(t0, bit_field3);
 
           // Allocate object with a slack.