Use the previous context link when checking context extension objects.

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 f0297a6fbb21b78fd434fc6620b52b357ea9cbfd..746d18c5d156bf0c0a1d86f8ea0d3903fea4f58d 100644
--- a/src/x64/full-codegen-x64.cc
+++ b/src/x64/full-codegen-x64.cc
@@ -1089,8 +1089,7 @@ void FullCodeGenerator::EmitLoadGlobalSlotCheckExtensions(
         __ j(not_equal, slow);
       }
       // Load next context in chain.
-      __ movq(temp, ContextOperand(context, Context::CLOSURE_INDEX));
-      __ movq(temp, FieldOperand(temp, JSFunction::kContextOffset));
+      __ movq(temp, ContextOperand(context, Context::PREVIOUS_INDEX));
       // Walk the rest of the chain without clobbering rsi.
       context = temp;
     }
@@ -1118,8 +1117,7 @@ void FullCodeGenerator::EmitLoadGlobalSlotCheckExtensions(
     __ cmpq(ContextOperand(temp, Context::EXTENSION_INDEX), Immediate(0));
     __ j(not_equal, slow);
     // Load next context in chain.
-    __ movq(temp, ContextOperand(temp, Context::CLOSURE_INDEX));
-    __ movq(temp, FieldOperand(temp, JSFunction::kContextOffset));
+    __ movq(temp, ContextOperand(temp, Context::PREVIOUS_INDEX));
     __ jmp(&next);
     __ bind(&fast);
   }
@@ -1151,8 +1149,7 @@ MemOperand FullCodeGenerator::ContextSlotOperandCheckExtensions(
                 Immediate(0));
         __ j(not_equal, slow);
       }
-      __ movq(temp, ContextOperand(context, Context::CLOSURE_INDEX));
-      __ movq(temp, FieldOperand(temp, JSFunction::kContextOffset));
+      __ movq(temp, ContextOperand(context, Context::PREVIOUS_INDEX));
       // Walk the rest of the chain without clobbering rsi.
       context = temp;
     }