Only reload libraries when they may have been modified.

runtime/include/dart_tools_api.h

 // Copyright (c) 2011, 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 INCLUDE_DART_TOOLS_API_H_
 #define INCLUDE_DART_TOOLS_API_H_
 
 #include "include/dart_api.h"
 
 /** \mainpage Dart Tools Embedding API Reference
@@ skipping 880 matching lines @@
  * \return Success if the arguments are well formed.  Otherwise, returns an
  *   error handle.
  */
 DART_EXPORT Dart_Handle Dart_ServiceSendDataEvent(const char* stream_id,
                                                   const char* event_kind,
                                                   const uint8_t* bytes,
                                                   intptr_t bytes_length);
 
 /*
  * ========
+ * Reload support
+ * ========
+ *
+ * These functions are used to implement reloading in the Dart VM.
+ * This is an experimental feature, so embedders should be prepared
+ * for these functions to change.
+ */
+
+/**
+ * A callback which determines whether the file at some url has been
+ * modified since some time.  If the file cannot be found, true should
+ * be returned.
+ */
+typedef bool (*Dart_FileModifiedCallback)(const char* url, int64_t since);
+
+DART_EXPORT Dart_Handle Dart_SetFileModifiedCallback(
+    Dart_FileModifiedCallback file_modified_callback);
+
+/*
+ * ========
  * Timeline
  * ========
  */
 
 /**
  * Returns a timestamp in microseconds. This timestamp is suitable for
  * passing into the timeline system.
  *
  * \return A timestamp that can be passed to the timeline system.
  */
@@ skipping 150 matching lines @@
  * \param start_recording See Dart_EmbedderTimelineStartRecording.
  * \param stop_recording See Dart_EmbedderTimelineStopRecording.
  *
  * NOTE: To avoid races, this should be called before Dart_Initialize.
  */
 DART_EXPORT void Dart_SetEmbedderTimelineCallbacks(
     Dart_EmbedderTimelineStartRecording start_recording,
     Dart_EmbedderTimelineStopRecording stop_recording);
 
 #endif  // INCLUDE_DART_TOOLS_API_H_