Use CHECK_ISOLATE instead of the more heavy DARTSCOPE for

runtime/vm/dart_api_impl.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 "include/dart_api.h"
 #include "include/dart_mirrors_api.h"
 #include "include/dart_native_api.h"
 
 #include "platform/assert.h"
 #include "vm/bigint_operations.h"
@@ skipping 487 matching lines @@
   Isolate* isolate = Isolate::Current();
   CHECK_ISOLATE(isolate);
   NoGCScope ngc;
   return Api::UnwrapHandle(obj1) == Api::UnwrapHandle(obj2);
 }
 
 
 DART_EXPORT Dart_Handle Dart_HandleFromPersistent(
     Dart_PersistentHandle object) {
   Isolate* isolate = Isolate::Current();
-  DARTSCOPE(isolate);
+  CHECK_ISOLATE(isolate);
   ApiState* state = isolate->api_state();
   ASSERT(state != NULL);
   ASSERT(state->IsValidPersistentHandle(object));
   return Api::NewHandle(isolate,
                         reinterpret_cast<PersistentHandle*>(object)->raw());
 }
 
 
 DART_EXPORT Dart_Handle Dart_HandleFromWeakPersistent(
     Dart_WeakPersistentHandle object) {
   Isolate* isolate = Isolate::Current();
-  DARTSCOPE(isolate);
+  CHECK_ISOLATE(isolate);
   ApiState* state = isolate->api_state();
   ASSERT(state != NULL);
   ASSERT(state->IsValidWeakPersistentHandle(object) ||
          state->IsValidPrologueWeakPersistentHandle(object));
   return Api::NewHandle(
       isolate, reinterpret_cast<FinalizablePersistentHandle*>(object)->raw());
 }
 
 
 DART_EXPORT Dart_PersistentHandle Dart_NewPersistentHandle(Dart_Handle object) {
@@ skipping 3806 matching lines @@
   }
   {
     NoGCScope no_gc;
     RawObject* raw_obj = obj.raw();
     isolate->heap()->SetPeer(raw_obj, peer);
   }
   return Api::Success();
 }
 
 }  // namespace dart