Change the behavior of open on files to not truncate by default

runtime/bin/dartutils.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 "bin/dartutils.h"
 
 #include "bin/file.h"
 #include "bin/globals.h"
 
 const char* DartUtils::kDartScheme = "dart:";
@@ skipping 112 matching lines @@
   // Calculate the canonical path.
   const char* canon_url_str = GetCanonicalPath(library_url_str, url_str);
   Dart_Handle canon_url = Dart_NewString(canon_url_str);
   free(const_cast<char*>(canon_url_str));
 
   return canon_url;
 }
 
 
 Dart_Handle DartUtils::ReadStringFromFile(const char* filename) {
-  File* file = File::Open(filename, false);
+  File* file = File::Open(filename, File::kRead);
   if (file == NULL) {
     const char* format = "Unable to open file: %s";
     intptr_t len = snprintf(NULL, 0, format, filename);
     // TODO(iposva): Allocate from the zone instead of leaking error string
     // here. On the other hand the binary is about the exit anyway.
     char* error_msg = reinterpret_cast<char*>(malloc(len + 1));
     snprintf(error_msg, len + 1, format, filename);
     return Dart_Error(error_msg);
   }
   intptr_t len = file->Length();
@@ skipping 69 matching lines @@
            path, File::PathSeparator(), filename);
 
   free(path);
   char* canonical_filename = File::GetCanonicalPath(absolute_filename);
   if (canonical_filename == NULL) {
     return absolute_filename;
   }
   free(absolute_filename);
   return canonical_filename;
 }