Initial work on computing SSA.

runtime/vm/flow_graph_builder.h

Index: runtime/vm/flow_graph_builder.h
diff --git a/runtime/vm/flow_graph_builder.h b/runtime/vm/flow_graph_builder.h
index 347da1346e7560a075cd68d62e4831346226b7d4..e3b3fc7493e254a95e48b6e249ef4936f3d88eab 100644
--- a/runtime/vm/flow_graph_builder.h
+++ b/runtime/vm/flow_graph_builder.h
@@ -52,6 +52,11 @@ class FlowGraphBuilder: public ValueObject {
                     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_;