Add flow graph printing into a .cfg file with flag --print-flow-graph-file.

vm/flow_graph_builder.cc

Index: vm/flow_graph_builder.cc
===================================================================
--- vm/flow_graph_builder.cc	(revision 8145)
+++ vm/flow_graph_builder.cc	(working copy)
@@ -24,6 +24,7 @@
             "Eliminate type checks when allowed by static type analysis");
 DEFINE_FLAG(bool, print_ast, false, "Print abstract syntax tree.");
 DEFINE_FLAG(bool, print_flow_graph, false, "Print the IR flow graph.");
+DEFINE_FLAG(bool, print_flow_graph_file, false, "Print the IR into a file.");
 DECLARE_FLAG(bool, enable_type_checks);
 
 
@@ -2301,14 +2302,20 @@
     GrowableArray<BitVector*> dominance_frontier;
     ComputeDominators(&preorder_block_entries_, &parent, &dominance_frontier);
   }
-  if (FLAG_print_flow_graph) {
+  if (FLAG_print_flow_graph || FLAG_print_flow_graph_file) {
     intptr_t length = postorder_block_entries_.length();
     GrowableArray<BlockEntryInstr*> reverse_postorder(length);
     for (intptr_t i = length - 1; i >= 0; --i) {
       reverse_postorder.Add(postorder_block_entries_[i]);
     }
-    FlowGraphPrinter printer(function, reverse_postorder);
-    printer.PrintBlocks();
+    if (FLAG_print_flow_graph) {
+      FlowGraphPrinter printer(function, reverse_postorder);
+      printer.PrintBlocks();
+    }
+    if (FLAG_print_flow_graph_file) {
+      FlowGraphVisualizer printer(function, reverse_postorder);
+      printer.PrintFunction();
+    }
   }
 }