Reduce CPU usage when no isolates need to be profiled.

runtime/bin/dartutils.h

 // 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.
 
 #ifndef BIN_DARTUTILS_H_
 #define BIN_DARTUTILS_H_
 
 #include "include/dart_api.h"
 #include "include/dart_native_api.h"
 
@@ skipping 524 matching lines @@
   uint8_t* Data() const { return cobject_->value.as_external_typed_data.data; }
   void* Peer() const { return cobject_->value.as_external_typed_data.peer; }
   Dart_WeakPersistentHandleFinalizer Callback() const {
     return cobject_->value.as_external_typed_data.callback;
   }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(CObjectExternalUint8Array);
 };
 
+
+class ScopedBlockingCall {
+ public:
+  ScopedBlockingCall() {
+    Dart_IsolateBlocked();
+  }
+
+  ~ScopedBlockingCall() {
+    Dart_IsolateUnblocked();
+  }
+};
+
 }  // namespace bin
 }  // namespace dart
 
 #endif  // BIN_DARTUTILS_H_