Make sure polymorphic element access creates non-replaying phis.

src/x64/lithium-x64.cc

Index: src/x64/lithium-x64.cc
diff --git a/src/x64/lithium-x64.cc b/src/x64/lithium-x64.cc
index 3dcc97f5fed95ca97e1d25f3ee48857fb26f1c21..189adbba29802a22315a32643d7f6f625d660189 100644
--- a/src/x64/lithium-x64.cc
+++ b/src/x64/lithium-x64.cc
@@ -814,11 +814,7 @@ void LChunkBuilder::DoBasicBlock(HBasicBlock* block, HBasicBlock* next_block) {
     HEnvironment* last_environment = pred->last_environment();
     for (int i = 0; i < block->phis()->length(); ++i) {
       HPhi* phi = block->phis()->at(i);
-      // TODO(mstarzinger): The length check below should actually not
-      // be necessary, but some array stubs already rely on it. This
-      // should be investigated and fixed.
-      if (phi->HasMergedIndex() &&
-          phi->merged_index() < last_environment->length()) {
+      if (phi->HasMergedIndex()) {
         last_environment->SetValueAt(phi->merged_index(), phi);
       }
     }