First step to SSA construction: Phi insertion.

vm/flow_graph_builder.h

Index: vm/flow_graph_builder.h
===================================================================
--- vm/flow_graph_builder.h	(revision 8546)
+++ vm/flow_graph_builder.h	(working copy)
@@ -52,6 +52,11 @@
                     GrowableArray<intptr_t>* parent,
                     GrowableArray<intptr_t>* label);
 
+  void InsertPhis(GrowableArray<BlockEntryInstr*>* preorder,
+                  GrowableArray<BitVector*>* assigned_vars,
+                  intptr_t var_count,
+                  GrowableArray<BitVector*>* dom_frontier);
+
   const ParsedFunction& parsed_function_;
   GrowableArray<BlockEntryInstr*> preorder_block_entries_;
   GrowableArray<BlockEntryInstr*> postorder_block_entries_;