Deal with unhandled exceptions the same way in all Dart api functions.

runtime/vm/parser.cc

 // 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.
 
 #include "vm/parser.h"
 
 #include "vm/bigint_operations.h"
 #include "vm/class_finalizer.h"
 #include "vm/compiler.h"
 #include "vm/compiler_stats.h"
@@ skipping 3082 matching lines @@
 Dart_Handle Parser::CallLibraryTagHandler(Dart_LibraryTag tag,
                                    intptr_t token_pos,
                                    const String& url) {
   Dart_LibraryTagHandler handler = Isolate::Current()->library_tag_handler();
   if (handler == NULL) {
     ErrorMsg(token_pos, "no library handler registered");
   }
   Dart_Handle result = handler(tag,
                                Api::NewLocalHandle(library_),
                                Api::NewLocalHandle(url));
-  if (!Dart_IsValid(result)) {
+  if (Dart_IsError(result)) {
     ErrorMsg(token_pos, "library handler failed: %s", Dart_GetError(result));
   }
   return result;
 }
 
 
 void Parser::ParseLibraryImport() {
   while (CurrentToken() == Token::kIMPORT) {
     intptr_t import_pos = token_index_;
     ConsumeToken();
@@ skipping 4152 matching lines @@
 }
 
 
 void Parser::SkipNestedExpr() {
   const bool saved_mode = SetAllowFunctionLiterals(true);
   SkipExpr();
   SetAllowFunctionLiterals(saved_mode);
 }
 
 }  // namespace dart