Use the previous context link when checking context extension objects.

src/ia32/full-codegen-ia32.cc

Index: src/ia32/full-codegen-ia32.cc
diff --git a/src/ia32/full-codegen-ia32.cc b/src/ia32/full-codegen-ia32.cc
index c727c0310ee9c6611ccd47a31fc275fd2ae4e380..8e8fcd25f9a05c72ee677b72a8a86f6203580204 100644
--- a/src/ia32/full-codegen-ia32.cc
+++ b/src/ia32/full-codegen-ia32.cc
@@ -1078,8 +1078,7 @@ void FullCodeGenerator::EmitLoadGlobalSlotCheckExtensions(
         __ j(not_equal, slow);
       }
       // Load next context in chain.
-      __ mov(temp, ContextOperand(context, Context::CLOSURE_INDEX));
-      __ mov(temp, FieldOperand(temp, JSFunction::kContextOffset));
+      __ mov(temp, ContextOperand(context, Context::PREVIOUS_INDEX));
       // Walk the rest of the chain without clobbering esi.
       context = temp;
     }
@@ -1106,8 +1105,7 @@ void FullCodeGenerator::EmitLoadGlobalSlotCheckExtensions(
     __ cmp(ContextOperand(temp, Context::EXTENSION_INDEX), Immediate(0));
     __ j(not_equal, slow);
     // Load next context in chain.
-    __ mov(temp, ContextOperand(temp, Context::CLOSURE_INDEX));
-    __ mov(temp, FieldOperand(temp, JSFunction::kContextOffset));
+    __ mov(temp, ContextOperand(temp, Context::PREVIOUS_INDEX));
     __ jmp(&next);
     __ bind(&fast);
   }
@@ -1139,8 +1137,7 @@ MemOperand FullCodeGenerator::ContextSlotOperandCheckExtensions(
                Immediate(0));
         __ j(not_equal, slow);
       }
-      __ mov(temp, ContextOperand(context, Context::CLOSURE_INDEX));
-      __ mov(temp, FieldOperand(temp, JSFunction::kContextOffset));
+      __ mov(temp, ContextOperand(context, Context::PREVIOUS_INDEX));
       // Walk the rest of the chain without clobbering esi.
       context = temp;
     }