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

runtime/bin/main.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 <stdlib.h>
 #include <string.h>
 #include <stdio.h>
 
 #include "include/dart_api.h"
 #include "include/dart_debugger_api.h"
@@ skipping 179 matching lines @@
 
   return Dart_SetStaticField(runtime_options_class,
                              native_name,
                              dart_arguments);
 }
 
 
 static void DumpPprofSymbolInfo() {
   if (generate_pprof_symbols_filename != NULL) {
     Dart_EnterScope();
-    File* pprof_file = File::Open(generate_pprof_symbols_filename, true);
+    File* pprof_file =
+        File::Open(generate_pprof_symbols_filename, File::kWriteTruncate);
     ASSERT(pprof_file != NULL);
     void* buffer;
     int buffer_size;
     Dart_GetPprofSymbolInfo(&buffer, &buffer_size);
     if (buffer_size > 0) {
       ASSERT(buffer != NULL);
       pprof_file->WriteFully(buffer, buffer_size);
     }
     delete pprof_file;  // Closes the file.
     Dart_ExitScope();
@@ skipping 286 matching lines @@
     return 255;  // Indicates we encountered an error.
   }
   free(canonical_script_name);
   Dart_ExitScope();
   // Dump symbol information for the profiler.
   DumpPprofSymbolInfo();
   // Shutdown the isolate.
   Dart_ShutdownIsolate();
   return 0;
 }