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

vm/isolate.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/isolate.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "lib/mirrors.h"
 #include "vm/compiler_stats.h"
@@ skipping 146 matching lines @@
       debugger_(NULL),
       long_jump_base_(NULL),
       timer_list_(),
       ast_node_id_(AstNode::kNoId),
       computation_id_(AstNode::kNoId),
       ic_data_array_(Array::null()),
       mutex_(new Mutex()),
       stack_limit_(0),
       saved_stack_limit_(0),
       message_handler_(NULL),
-      spawn_data_(NULL) {
-}
+      spawn_data_(NULL),
+      flow_graph_file_(NULL) { }
 
 
 Isolate::~Isolate() {
   delete [] name_;
   delete heap_;
   delete object_store_;
   delete api_state_;
   delete stub_code_;
   delete debugger_;
   delete mutex_;
@@ skipping 285 matching lines @@
 
 
 void Isolate::VisitWeakPersistentHandles(HandleVisitor* visitor,
                                          bool visit_prologue_weak_handles) {
   if (api_state() != NULL) {
     api_state()->VisitWeakHandles(visitor, visit_prologue_weak_handles);
   }
 }
 
 }  // namespace dart