Start using Dart_PropagateError in the runtime/bin directory.

runtime/include/dart_api.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 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 1921 matching lines @@
  */
 DART_EXPORT bool Dart_IsLibrary(Dart_Handle object);
 
 /**
  * Lookup a class by name from a Library.
  *
  * \return If no error occurs, the Library is returned. Otherwise an
  *   error handle is returned.
  */
 DART_EXPORT Dart_Handle Dart_GetClass(Dart_Handle library, Dart_Handle name);
+// TODO(turnidge): Consider returning Dart_Null() when the class is
+// not found to distinguish that from a true error case.
 
 DART_EXPORT Dart_Handle Dart_LibraryUrl(Dart_Handle library);
 
 DART_EXPORT Dart_Handle Dart_LookupLibrary(Dart_Handle url);
+// TODO(turnidge): Consider returning Dart_Null() when the library is
+// not found to distinguish that from a true error case.
 
 DART_EXPORT Dart_Handle Dart_LoadLibrary(Dart_Handle url,
                                          Dart_Handle source,
                                          Dart_Handle import_map);
 
 
 DART_EXPORT Dart_Handle Dart_LibraryImportLibrary(Dart_Handle library,
                                                   Dart_Handle import);
 
 DART_EXPORT Dart_Handle Dart_LoadSource(Dart_Handle library,
@@ skipping 16 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_