Enable redundancy elimination for array loads.

runtime/vm/flow_graph_optimizer.h

Index: runtime/vm/flow_graph_optimizer.h
===================================================================
--- runtime/vm/flow_graph_optimizer.h	(revision 13809)
+++ runtime/vm/flow_graph_optimizer.h	(working copy)
@@ -155,10 +155,12 @@
 // on the dominator tree.
 class DominatorBasedCSE : public AllStatic {
  public:
-  static void Optimize(FlowGraph* graph);
+  // Return true, if the optimization changed the flow graph.
+  // False, if nothing changed.
+  static bool Optimize(FlowGraph* graph);
 
  private:
-  static void OptimizeRecursive(
+  static bool OptimizeRecursive(
       BlockEntryInstr* entry,
       DirectChainedHashMap<Instruction*>* map);
 };