Reuse the top ApiLocalScope so that we do not allocate and free an ApiLocalScope

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 1054 matching lines @@
 }
 
 
 // --- Scopes ----
 
 DART_EXPORT void Dart_EnterScope() {
   Isolate* isolate = Isolate::Current();
   CHECK_ISOLATE(isolate);
   ApiState* state = isolate->api_state();
   ASSERT(state != NULL);
-  ApiLocalScope* new_scope = new ApiLocalScope(state->top_scope(),
-                                               isolate->top_exit_frame_info());
-  ASSERT(new_scope != NULL);
+  ApiLocalScope* new_scope = state->reusable_scope();
+  if (new_scope == NULL) {
+    new_scope = new ApiLocalScope(state->top_scope(),
+                                  isolate->top_exit_frame_info());
+    ASSERT(new_scope != NULL);
+  } else {
+    new_scope->Reinit(isolate,
+                      state->top_scope(),
+                      isolate->top_exit_frame_info());
+    state->set_reusable_scope(NULL);
+  }
   state->set_top_scope(new_scope);  // New scope is now the top scope.
 }
 
 
 DART_EXPORT void Dart_ExitScope() {
   Isolate* isolate = Isolate::Current();
   CHECK_ISOLATE_SCOPE(isolate);
   ApiState* state = isolate->api_state();
   ApiLocalScope* scope = state->top_scope();
-
+  ApiLocalScope* reusable_scope = state->reusable_scope();
   state->set_top_scope(scope->previous());  // Reset top scope to previous.
-  delete scope;  // Free up the old scope which we have just exited.
+  if (reusable_scope == NULL) {
+    scope->Reset(isolate);  // Reset the old scope which we just exited.
+    state->set_reusable_scope(scope);
+  } else {
+    ASSERT(reusable_scope != scope);
+    delete scope;
+  }
 }
 
 
 DART_EXPORT uint8_t* Dart_ScopeAllocate(intptr_t size) {
   Zone* zone;
   Isolate* isolate = Isolate::Current();
   if (isolate != NULL) {
     ApiState* state = isolate->api_state();
     if (state == NULL) return NULL;
     ApiLocalScope* scope = state->top_scope();
@@ skipping 2904 matching lines @@
   }
   {
     NoGCScope no_gc;
     RawObject* raw_obj = obj.raw();
     isolate->heap()->SetPeer(raw_obj, peer);
   }
   return Api::Success();
 }
 
 }  // namespace dart