Regularize some naming to make BUILD.gn files easier to write.

runtime/bin/builtin.cc

 // 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.
 
 #include <stdio.h>
 
 #include "include/dart_api.h"
 
 #include "bin/builtin.h"
 #include "bin/dartutils.h"
 
 namespace dart {
 namespace bin {
 
 Builtin::builtin_lib_props Builtin::builtin_libraries_[] = {
   /* { url_, source_, patch_url_, patch_source_, has_natives_ } */
-  { DartUtils::kBuiltinLibURL, builtin_source_paths_, NULL, NULL, true },
+  { DartUtils::kBuiltinLibURL, _builtin_source_paths_, NULL, NULL, true },
   { DartUtils::kIOLibURL, io_source_paths_,
     DartUtils::kIOLibPatchURL, io_patch_paths_, true },
 };
 
 
 // Patch all the specified patch files in the array 'patch_files' into the
 // library specified in 'library'.
 static void LoadPatchFiles(Dart_Handle library,
                            const char* patch_uri,
                            const char** patch_files) {
@@ skipping 83 matching lines @@
   Dart_Handle library = Dart_LookupLibrary(url);
   if (Dart_IsError(library)) {
     library = LoadLibrary(url, id);
   }
   DART_CHECK_VALID(library);
   return library;
 }
 
 }  // namespace bin
 }  // namespace dart