[vm, gc] Require a safepoint for heap iteration.

runtime/vm/debugger_api_impl_test.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 "include/dart_mirrors_api.h"
 #include "include/dart_tools_api.h"
 #include "platform/assert.h"
 #include "vm/dart_api_impl.h"
 #include "vm/lockers.h"
 #include "vm/unit_test.h"
@@ skipping 983 matching lines @@
   Dart_GetStackTrace(&trace);
   Dart_ActivationFrame frame;
   Dart_Handle res = Dart_GetActivationFrame(trace, 0, &frame);
   EXPECT_VALID(res);
   Dart_Handle func_name;
   intptr_t line_number = -1;
   res = Dart_ActivationFrameInfo(frame, &func_name, NULL, &line_number, NULL);
   EXPECT_NE(-1, line_number);
   if (verbose) OS::Print("Hit line %" Pd "\n", line_number);
 
+  TransitionNativeToVM transition(Thread::Current());
   VerifyPointersVisitor::VerifyPointers();
 }
 
 static void NoopNativeFunction(Dart_NativeArguments args) {
   Dart_EnterScope();
   Dart_SetReturnValue(args, Dart_True());
   Dart_ExitScope();
 }
 
 static Dart_NativeFunction NoopNativeResolver(Dart_Handle name,
@@ skipping 1271 matching lines @@
       " null, 5, 17, 5, 18, 9, 19, 12,"
       " null, 6, 21, 1,"
       " null, 8, 24, 1, 25, 5, 26, 6, 27, 8,"
       " null, 9, 29, 1]",
       tokens_cstr);
 }
 
 #endif
 
 }  // namespace dart