Simplify and fix code aging.

src/x64/full-codegen-x64.cc

Index: src/x64/full-codegen-x64.cc
diff --git a/src/x64/full-codegen-x64.cc b/src/x64/full-codegen-x64.cc
index 1e16c666b2f87bbca80d99a912276173a0ea8371..650337a29599fc09e685b0df7b08624e70e5b578 100644
--- a/src/x64/full-codegen-x64.cc
+++ b/src/x64/full-codegen-x64.cc
@@ -138,8 +138,6 @@ void FullCodeGenerator::Generate() {
   // function calls.
   if (!info->is_classic_mode() || info->is_native()) {
     Label ok;
-    Label begin;
-    __ bind(&begin);
     __ testq(rcx, rcx);
     __ j(zero, &ok, Label::kNear);
     // +1 for return address.
@@ -147,8 +145,6 @@ void FullCodeGenerator::Generate() {
     __ LoadRoot(kScratchRegister, Heap::kUndefinedValueRootIndex);
     __ movq(Operand(rsp, receiver_offset), kScratchRegister);
     __ bind(&ok);
-    ASSERT(!FLAG_age_code ||
-           (kSizeOfFullCodegenStrictModePrologue == ok.pos() - begin.pos()));
   }
 
   // Open a frame scope to indicate that there is a frame on the stack.  The
@@ -156,6 +152,7 @@ void FullCodeGenerator::Generate() {
   // the frame (that is done below).
   FrameScope frame_scope(masm_, StackFrame::MANUAL);
 
+  info->set_prologue_offset(masm_->pc_offset());
   __ push(rbp);  // Caller's frame pointer.
   __ movq(rbp, rsp);
   __ push(rsi);  // Callee's context.