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

runtime/bin/gen_snapshot.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.
 
 // Generate a snapshot file after loading all the scripts specified on the
 // command line.
 
 #include <stdlib.h>
 #include <string.h>
 #include <stdio.h>
@@ skipping 84 matching lines @@
   Dart_Handle result;
   Dart_EnterScope();
 
   ASSERT(snapshot_filename != NULL);
 
   // If a file is specified on the command line, load it up before a snapshot
   // is created.
   if (script_name != NULL) {
     // Load the specified script.
     Dart_Handle library = LoadSnapshotCreationScript(script_name);
-    if (!Dart_IsValid(library)) {
+    if (Dart_IsError(library)) {
       const char* err_msg = Dart_GetError(library);
       fprintf(stderr, "Errors encountered while loading script: %s\n", err_msg);
       Dart_ExitScope();
       exit(255);
     }
 
     if (!Dart_IsLibrary(library)) {
       fprintf(stderr,
               "Expected a library when loading script: %s",
               script_name);
       Dart_ExitScope();
       exit(255);
     }
   } else {
     // Implicitly load builtin library.
     Builtin_LoadLibrary();
     // Setup the native resolver for built in library functions.
     Builtin_SetNativeResolver();
   }
 
   uint8_t* buffer = NULL;
   intptr_t size = 0;
   // First create the snapshot.
   result = Dart_CreateSnapshot(&buffer, &size);
-  if (!Dart_IsValid(result)) {
+  if (Dart_IsError(result)) {
     const char* err_msg = Dart_GetError(result);
     fprintf(stderr, "Error while creating snapshot: %s\n", err_msg);
     Dart_ExitScope();
     exit(255);
   }
   // Now write the snapshot out to specified file and exit.
   WriteSnapshotFile(buffer, size);
   Dart_ExitScope();
   return data;
 }
@@ skipping 34 matching lines @@
   // and writes out a snapshot.
   Dart_Isolate isolate = Dart_CreateIsolate(NULL, script_name);
   if (isolate == NULL) {
     return 255;
   }
 
   // Shutdown the isolate.
   Dart_ShutdownIsolate();
   return 0;
 }