Share optimized code for closures.

src/x64/lithium-codegen-x64.cc

Index: src/x64/lithium-codegen-x64.cc
===================================================================
--- src/x64/lithium-codegen-x64.cc	(revision 11812)
+++ src/x64/lithium-codegen-x64.cc	(working copy)
@@ -367,7 +367,10 @@
   int height = translation_size - environment->parameter_count();
 
   WriteTranslation(environment->outer(), translation);
-  int closure_id = DefineDeoptimizationLiteral(environment->closure());
+  int closure_id = *info()->closure() != *environment->closure()
+      ? DefineDeoptimizationLiteral(environment->closure())
+      : Translation::kSelfLiteralId;
+
   switch (environment->frame_type()) {
     case JS_FUNCTION:
       translation->BeginJSFrame(environment->ast_id(), closure_id, height);
@@ -2731,7 +2734,7 @@
 
 void LCodeGen::DoThisFunction(LThisFunction* instr) {
   Register result = ToRegister(instr->result());
-  __ LoadHeapObject(result, instr->hydrogen()->closure());
+  __ movq(result, Operand(rbp, JavaScriptFrameConstants::kFunctionOffset));
 }