Fix two x64 code generation bugs introduced by const context slot code from r10244

TEST=mjsunit debug tests pass again.
Review URL: http://codereview.chromium.org/8932014

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10249 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/x64/lithium-codegen-x64.cc

@@ -2074,7 +2074,7 @@ void LCodeGen::DoLoadContextSlot(LLoadContextSlot* instr) {
     } else {
       Label is_not_hole;
       __ j(not_equal, &is_not_hole, Label::kNear);
-      __ movq(result, factory()->undefined_value(), RelocInfo::NONE);
+      __ LoadRoot(result, Heap::kUndefinedValueRootIndex);
       __ bind(&is_not_hole);
     }
   }
@@ -2093,7 +2093,7 @@ void LCodeGen::DoStoreContextSlot(LStoreContextSlot* instr) {
     if (instr->hydrogen()->DeoptimizesOnHole()) {
       DeoptimizeIf(equal, instr->environment());
     } else {
-      __ j(not_equal, &skip_assignment, Label::kNear);
+      __ j(not_equal, &skip_assignment);
     }
   }
   __ movq(target, value);