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

runtime/bin/file.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/file.h"
 
 #include "bin/builtin.h"
 #include "bin/dartutils.h"
 
 #include "include/dart_api.h"
@@ skipping 23 matching lines @@
       return false;
     }
     remaining -= bytes_read;  // Reduce the number of remaining bytes.
     current_buffer += bytes_read;  // Move the buffer forward.
   }
   return true;
 }
 
 
 void FUNCTION_NAME(File_Open)(Dart_NativeArguments args) {
+  // These values have to be kept in sync with the mode values of
+  // FileMode.READ, FileMode.WRITE and FileMode.APPEND in file.dart.
+  static const int kRead = 0;
+  static const int kWrite = 1;
+  static const int kAppend = 2;
+
   Dart_EnterScope();
   const char* filename =
       DartUtils::GetStringValue(Dart_GetNativeArgument(args, 0));
-  bool writable = DartUtils::GetBooleanValue(Dart_GetNativeArgument(args, 1));
-  File* file = File::Open(filename, writable);
+  int mode = DartUtils::GetIntegerValue(Dart_GetNativeArgument(args, 1));
+  ASSERT(mode == kRead || mode == kWrite || mode == kAppend);
+  File::FileOpenMode file_mode = File::kRead;
+  if (mode == kWrite) {
+    file_mode = File::kWriteTruncate;
+  }
+  if (mode == kAppend) {
+    file_mode = File::kWrite;
+  }
+  File* file = File::Open(filename, file_mode);
   Dart_SetReturnValue(args, Dart_NewInteger(reinterpret_cast<intptr_t>(file)));
   Dart_ExitScope();
 }
 
 
 void FUNCTION_NAME(File_Exists)(Dart_NativeArguments args) {
   Dart_EnterScope();
   const char* filename =
       DartUtils::GetStringValue(Dart_GetNativeArgument(args, 0));
   bool exists = File::Exists(filename);
@@ skipping 244 matching lines @@
   Dart_EnterScope();
   const char* str =
       DartUtils::GetStringValue(Dart_GetNativeArgument(args, 0));
   char* path = File::GetCanonicalPath(str);
   if (path != NULL) {
     Dart_SetReturnValue(args, Dart_NewString(path));
     free(path);
   }
   Dart_ExitScope();
 }