Implement proper scoping for "this" in arrow functions

src/x64/lithium-codegen-x64.cc

Index: src/x64/lithium-codegen-x64.cc
diff --git a/src/x64/lithium-codegen-x64.cc b/src/x64/lithium-codegen-x64.cc
index 383795c8a0784134880d27122f34d13510931b3d..41683d4a518fb1d14aca629c50ce9a5c8f09401d 100644
--- a/src/x64/lithium-codegen-x64.cc
+++ b/src/x64/lithium-codegen-x64.cc
@@ -130,7 +130,8 @@ bool LCodeGen::GeneratePrologue() {
     // when called as functions (without an explicit receiver object).
     if (info_->this_has_uses() &&
         info_->strict_mode() == SLOPPY &&
-        !info_->is_native()) {
+        !info_->is_native() &&
+        info_->scope()->has_this_declaration()) {
       Label ok;
       StackArgumentsAccessor args(rsp, scope()->num_parameters());
       __ movp(rcx, args.GetReceiverOperand());
@@ -212,8 +213,9 @@ bool LCodeGen::GeneratePrologue() {
 
     // Copy any necessary parameters into the context.
     int num_parameters = scope()->num_parameters();
-    for (int i = 0; i < num_parameters; i++) {
-      Variable* var = scope()->parameter(i);
+    int first_parameter = scope()->has_this_declaration() ? -1 : 0;
+    for (int i = first_parameter; i < num_parameters; i++) {
+      Variable* var = (i == -1) ? scope()->receiver() : scope()->parameter(i);
       if (var->IsContextSlot()) {
         int parameter_offset = StandardFrameConstants::kCallerSPOffset +
             (num_parameters - 1 - i) * kPointerSize;