Simplify and fix code aging.

src/mips/lithium-codegen-mips.cc

Index: src/mips/lithium-codegen-mips.cc
diff --git a/src/mips/lithium-codegen-mips.cc b/src/mips/lithium-codegen-mips.cc
index e19caf34c2a901be98b7a9eb414fcb59c9e10c35..56a89e03baf3e3d86a8a9f64fb7fefe21a700f47 100644
--- a/src/mips/lithium-codegen-mips.cc
+++ b/src/mips/lithium-codegen-mips.cc
@@ -136,17 +136,15 @@ bool LCodeGen::GeneratePrologue() {
   // function calls.
   if (!info_->is_classic_mode() || info_->is_native()) {
     Label ok;
-    Label begin;
-    __ bind(&begin);
     __ Branch(&ok, eq, t1, Operand(zero_reg));
 
     int receiver_offset = scope()->num_parameters() * kPointerSize;
     __ LoadRoot(a2, Heap::kUndefinedValueRootIndex);
     __ sw(a2, MemOperand(sp, receiver_offset));
     __ bind(&ok);
-    ASSERT_EQ(kSizeOfOptimizedStrictModePrologue, ok.pos() - begin.pos());
   }
 
+  info()->set_prologue_offset(masm_->pc_offset());
   // The following three instructions must remain together and unmodified for
   // code aging to work properly.
   __ Push(ra, fp, cp, a1);