Fix --break_at_isolate_spawn. Starting in r44655 implicit static closure function are not themselve…

runtime/vm/isolate.cc

 // Copyright (c) 2013, 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 "platform/json.h"
 #include "vm/code_observers.h"
@@ skipping 1173 matching lines @@
     Object& result = Object::Handle();
     result = state->ResolveFunction();
     bool is_spawn_uri = state->is_spawn_uri();
     if (result.IsError()) {
       StoreError(isolate, result);
       return false;
     }
     ASSERT(result.IsFunction());
     Function& func = Function::Handle(isolate);
     func ^= result.raw();
-    func = func.ImplicitClosureFunction();
 
     // TODO(turnidge): Currently we need a way to force a one-time
     // breakpoint for all spawned isolates to support isolate
     // debugging.  Remove this once the vmservice becomes the standard
-    // way to debug.
+    // way to debug. Set the breakpoint on the static function instead
+    // of its implicit closure function because that latter is merely
+    // a dispatcher that is marked as undebuggable.
     if (FLAG_break_at_isolate_spawn) {
       isolate->debugger()->OneTimeBreakAtEntry(func);
     }
 
+    func = func.ImplicitClosureFunction();
+
     const Array& capabilities = Array::Handle(Array::New(2));
     Capability& capability = Capability::Handle();
     capability = Capability::New(isolate->pause_capability());
     capabilities.SetAt(0, capability);
     // Check whether this isolate should be started in paused state.
     if (state->paused()) {
       bool added = isolate->AddResumeCapability(capability);
       ASSERT(added);  // There should be no pending resume capabilities.
       isolate->message_handler()->increment_paused();
     }
@@ skipping 759 matching lines @@
                            serialized_message_, serialized_message_len_);
 }
 
 
 void IsolateSpawnState::Cleanup() {
   SwitchIsolateScope switch_scope(I);
   Dart::ShutdownIsolate();
 }
 
 }  // namespace dart