If an unhandled exception occurs in Dart_RunLoop, pass it out to the caller.

runtime/include/dart_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_API_H_
 #define INCLUDE_DART_API_H_
 
 /** \mainpage Dart Embedding API Reference
  *
  * Dart is a class-based programming language for creating structured
@@ skipping 457 matching lines @@
  * Processes any incoming messages for the current isolate.
  *
  * This function may only be used when the embedder has not provided
  * an alternate message delivery mechanism with
  * Dart_SetMessageCallbacks. It is provided for convenience.
  *
  * This function waits for incoming messages for the current
  * isolate. As new messages arrive, they are handled using
  * Dart_HandleMessage. The routine exits when all ports to the
  * current isolate are closed.
+ *
+ * \return A valid handle if the run loop exited successfully.  If an
+ *   exception or other error occurs while processing messages, an
+ *   error handle is returned.
  */
 DART_EXPORT Dart_Handle Dart_RunLoop();
 // TODO(turnidge): Should this be removed from the public api?
 
 /**
  * Gets the main port id for the current isolate.
  */
 DART_EXPORT Dart_Port Dart_GetMainPortId();
 
 /**
@@ skipping 859 matching lines @@
 
 // --- Profiling support ----
 
 // External pprof support for gathering and dumping symbolic
 // information that can be used for better profile reports for
 // dynamically generated code.
 DART_EXPORT void Dart_InitPprofSupport();
 DART_EXPORT void Dart_GetPprofSymbolInfo(void** buffer, int* buffer_size);
 
 #endif  // INCLUDE_DART_API_H_