Revert of Resolve references to "this" the same way as normal variables

src/mips64/full-codegen-mips64.cc

Index: src/mips64/full-codegen-mips64.cc
diff --git a/src/mips64/full-codegen-mips64.cc b/src/mips64/full-codegen-mips64.cc
index 7cb671f5f3aab38ee2163c820639f4e06d349d4c..0e3f0725e6360671947716dd01174da5575199b0 100644
--- a/src/mips64/full-codegen-mips64.cc
+++ b/src/mips64/full-codegen-mips64.cc
@@ -135,7 +135,7 @@
   // global proxy when called as functions (without an explicit receiver
   // object).
   if (is_sloppy(info->language_mode()) && !info->is_native() &&
-      info->MayUseThis() && info->scope()->has_this_declaration()) {
+      info->MayUseThis()) {
     Label ok;
     int receiver_offset = info->scope()->num_parameters() * kPointerSize;
     __ ld(at, MemOperand(sp, receiver_offset));
@@ -222,9 +222,8 @@
     __ sd(v0, MemOperand(fp, StandardFrameConstants::kContextOffset));
     // Copy any necessary parameters into the context.
     int num_parameters = info->scope()->num_parameters();
-    int first_parameter = info->scope()->has_this_declaration() ? -1 : 0;
-    for (int i = first_parameter; i < num_parameters; i++) {
-      Variable* var = (i == -1) ? scope()->receiver() : scope()->parameter(i);
+    for (int i = 0; i < num_parameters; i++) {
+      Variable* var = scope()->parameter(i);
       if (var->IsContextSlot()) {
         int parameter_offset = StandardFrameConstants::kCallerSPOffset +
                                  (num_parameters - 1 - i) * kPointerSize;
@@ -3040,9 +3039,8 @@
   __ ld(a6, MemOperand(fp, JavaScriptFrameConstants::kFunctionOffset));
 
   // a5: the receiver of the enclosing function.
-  Variable* this_var = scope()->LookupThis();
-  DCHECK_NOT_NULL(this_var);
-  __ ld(a5, VarOperand(this_var, a5));
+  int receiver_offset = 2 + info_->scope()->num_parameters();
+  __ ld(a5, MemOperand(fp, receiver_offset * kPointerSize));
 
   // a4: the language mode.
   __ li(a4, Operand(Smi::FromInt(language_mode())));