Fix slack tracking when instance prototype changes.

src/mips/stub-cache-mips.cc

Index: src/mips/stub-cache-mips.cc
diff --git a/src/mips/stub-cache-mips.cc b/src/mips/stub-cache-mips.cc
index ba1d17722db2b8c294af9d3502af238857c1ef05..bd15775d4b000f8e8a0478526b3c8c0c3939a5ce 100644
--- a/src/mips/stub-cache-mips.cc
+++ b/src/mips/stub-cache-mips.cc
@@ -3453,7 +3453,7 @@ Handle<Code> ConstructStubCompiler::CompileConstructStub(
   // t7: undefined
   __ lbu(a3, FieldMemOperand(a2, Map::kInstanceTypeOffset));
   __ Check(ne, "Function constructed by construct stub.",
-      a3, Operand(JS_FUNCTION_TYPE));
+           a3, Operand(JS_FUNCTION_TYPE));
 #endif
 
   // Now allocate the JSObject in new space.
@@ -3461,7 +3461,13 @@ Handle<Code> ConstructStubCompiler::CompileConstructStub(
   // a1: constructor function
   // a2: initial map
   // t7: undefined
+  ASSERT(function->has_initial_map());
   __ lbu(a3, FieldMemOperand(a2, Map::kInstanceSizeOffset));
+#ifdef DEBUG
+  int instance_size = function->initial_map()->instance_size();
+  __ Check(eq, "Instance size of initial map changed.",
+           a3, Operand(instance_size >> kPointerSizeLog2));
+#endif
   __ AllocateInNewSpace(a3, t4, t5, t6, &generic_stub_call, SIZE_IN_WORDS);
 
   // Allocated the JSObject, now initialize the fields. Map is set to initial
@@ -3524,7 +3530,6 @@ Handle<Code> ConstructStubCompiler::CompileConstructStub(
   }
 
   // Fill the unused in-object property fields with undefined.
-  ASSERT(function->has_initial_map());
   for (int i = shared->this_property_assignments_count();
        i < function->initial_map()->inobject_properties();
        i++) {