Use HInstructionIterator more broadly for hydrogen.

src/hydrogen-gvn.cc

Index: src/hydrogen-gvn.cc
diff --git a/src/hydrogen-gvn.cc b/src/hydrogen-gvn.cc
index b27b86f14b623da9a96cc395fe21219d64b8c031..d9dd740c34a03f4ed432eda35c6fdd107fd7ea63 100644
--- a/src/hydrogen-gvn.cc
+++ b/src/hydrogen-gvn.cc
@@ -397,17 +397,16 @@ void HGlobalValueNumberer::ComputeBlockSideEffects() {
   for (int i = graph_->blocks()->length() - 1; i >= 0; --i) {
     // Compute side effects for the block.
     HBasicBlock* block = graph_->blocks()->at(i);
-    HInstruction* instr = block->first();
     int id = block->block_id();
     GVNFlagSet side_effects;
-    while (instr != NULL) {
+    for (HInstructionIterator it(block); !it.Done(); it.Advance()) {
+      HInstruction* instr = it.Current();
       side_effects.Add(instr->ChangesFlags());
       if (instr->IsSoftDeoptimize()) {
         block_side_effects_[id].RemoveAll();
         side_effects.RemoveAll();
         break;
       }
-      instr = instr->next();
     }
     block_side_effects_[id].Add(side_effects);