MIPS64: Fix port of Refactor Map::ConstructionCount.

Port 35ff259b.

BUG=

Review URL: https://codereview.chromium.org/756383005

Cr-Commit-Position: refs/heads/master@{#25693}

src/mips64/builtins-mips64.cc

@@ -395,9 +395,9 @@ static void Generate_JSConstructStubHelper(MacroAssembler* masm,
         __ CallRuntime(Runtime::kFinalizeInstanceSize, 1);
 
         __ Pop(a1, a2);
-        // Slack tracking counter is kNoSlackTracking after runtime call.
-        DCHECK(JSFunction::kNoSlackTracking == 0);
-        __ mov(a6, zero_reg);
+        // Slack tracking counter is Map::kSlackTrackingCounterEnd after runtime
+        // call.
+        __ li(a6, Map::kSlackTrackingCounterEnd);
 
         __ bind(&allocate);
       }