- Create isolate specific resuable handles and use them in the hot lookup paths.

runtime/vm/handles.cc

Index: runtime/vm/handles.cc
===================================================================
--- runtime/vm/handles.cc	(revision 24061)
+++ runtime/vm/handles.cc	(working copy)
@@ -121,6 +121,25 @@
 NoHandleScope::~NoHandleScope() {
   isolate()->DecrementNoHandleScopeDepth();
 }
+
+
+ReusableHandleScope::ReusableHandleScope(BaseIsolate* isolate)
+    : StackResource(isolate) {
+  ASSERT(!isolate->reusable_handle_scope_active());
+  isolate->set_reusable_handle_scope_active(true);
+}
+
+
+ReusableHandleScope::ReusableHandleScope() : StackResource(Isolate::Current()) {
+  ASSERT(!isolate()->reusable_handle_scope_active());
+  isolate()->set_reusable_handle_scope_active(true);
+}
+
+
+ReusableHandleScope::~ReusableHandleScope() {
+  ASSERT(isolate()->reusable_handle_scope_active());
+  isolate()->set_reusable_handle_scope_active(false);
+}
 #endif  // defined(DEBUG)
 
 }  // namespace dart