VM: Move redundancy elimination phases into a separate file.

runtime/vm/flow_graph.h

Index: runtime/vm/flow_graph.h
diff --git a/runtime/vm/flow_graph.h b/runtime/vm/flow_graph.h
index cf62e82dde8dcb834b4dd0083252702b77355f89..970a7a0386c8a66289ba3d5cd08e2cb2fa0abde2 100644
--- a/runtime/vm/flow_graph.h
+++ b/runtime/vm/flow_graph.h
@@ -144,6 +144,12 @@ class FlowGraph : public ZoneAllocated {
     return BlockIterator(postorder());
   }
 
+  void EnsureSSATempIndex(Definition* defn, Definition* replacement);
+
+  void ReplaceCurrentInstruction(ForwardInstructionIterator* iterator,
+                                 Instruction* current,
+                                 Instruction* replacement);
+
   intptr_t current_ssa_temp_index() const { return current_ssa_temp_index_; }
   void set_current_ssa_temp_index(intptr_t index) {
     current_ssa_temp_index_ = index;