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 0f0d136b91d78abeef55792e200c6461fbfe7820..b8d3dff80a8bd77bf60e0b42135872d6a6293e60 100644
--- a/src/x64/lithium-codegen-x64.cc
+++ b/src/x64/lithium-codegen-x64.cc
@@ -130,7 +130,7 @@ bool LCodeGen::GeneratePrologue() {
     // Sloppy mode functions need to replace the receiver with the global proxy
     // when called as functions (without an explicit receiver object).
     if (info_->this_has_uses() && is_sloppy(info_->language_mode()) &&
-        !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 +212,9 @@ 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;