Implement automatic loading of dart:core_native_fields library

bin/gen_snapshot.cc

Index: bin/gen_snapshot.cc
===================================================================
--- bin/gen_snapshot.cc	(revision 1545)
+++ bin/gen_snapshot.cc	(working copy)
@@ -93,36 +93,26 @@
 static void* SnapshotCreateCallback(void* data) {
   const char* script_name = reinterpret_cast<const char*>(data);
   Dart_Handle result;
+  Dart_Handle library;
   Dart_EnterScope();
 
   ASSERT(snapshot_filename != NULL);
 
-  // If a file is specified on the command line, load it up before a snapshot
-  // is created.
+  // Load up the script before a snapshot is created.
   if (script_name != NULL) {
     // Load the specified script.
-    Dart_Handle library = LoadSnapshotCreationScript(script_name);
-    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);
-    }
+    library = LoadSnapshotCreationScript(script_name);
   } else {
-    // Implicitly load builtin library.
-    Builtin_LoadLibrary();
-    // Setup the native resolver for built in library functions.
-    Builtin_SetNativeResolver();
+    // This is a generic dart snapshot which needs builtin library setup.
+    library = Builtin_LoadLibrary();
   }
-
+  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);
+  }
+  ASSERT(Dart_IsLibrary(library));
   uint8_t* buffer = NULL;
   intptr_t size = 0;
   // First create the snapshot.