Revert r9253 because of dartium test failures

vm/flow_graph_builder.h

Index: vm/flow_graph_builder.h
===================================================================
--- vm/flow_graph_builder.h	(revision 9254)
+++ vm/flow_graph_builder.h	(working copy)
@@ -114,13 +114,9 @@
 
   // Append a graph fragment to this graph.  Assumes this graph is open.
   void Append(const EffectGraphVisitor& other_fragment);
-  // Append a single instruction.  Assumes this graph is open. Can not be a
-  // block entry instruction.
+  // Append a single instruction.  Assumes this graph is open.
   void AddInstruction(Instruction* instruction);
 
-  // Append a new block entry to the graph.
-  void AddBlockEntry(BlockEntryInstr* successor);
-
   // Append a 'diamond' branch and join to this graph, depending on which
   // parts are reachable.  Assumes this graph is open.
   void Join(const TestGraphVisitor& test_fragment,