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

runtime/bin/file_test.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 "vm/assert.h"
 #include "vm/globals.h"
 #include "vm/unit_test.h"
 
 
 // Helper method to be able to run the test from the runtime
 // directory, or the top directory.
 static const char* GetFileName(const char* name) {
   if (File::Exists(name)) {
     return name;
   } else {
     static const int kRuntimeLength = strlen("runtime/");
     return name + kRuntimeLength;
   }
 }
 
 
 UNIT_TEST_CASE(Read) {
   const char* kFilename = GetFileName("runtime/bin/file_test.cc");
-  File* file = File::Open(kFilename, false);
+  File* file = File::Open(kFilename, File::kRead);
   EXPECT(file != NULL);
   EXPECT_STREQ(kFilename, file->name());
   char buffer[16];
   buffer[0] = '\0';
   EXPECT(file->ReadFully(buffer, 13));  // ReadFully returns true.
   buffer[13] = '\0';
   EXPECT_STREQ("// Copyright ", buffer);
   EXPECT(!file->WriteByte(1));  // Cannot write to a read-only file.
   delete file;
 }
 
 
 UNIT_TEST_CASE(FileLength) {
   const char* kFilename =
       GetFileName("runtime/tests/vm/data/fixed_length_file");
-  File* file = File::Open(kFilename, false);
+  File* file = File::Open(kFilename, File::kRead);
   EXPECT(file != NULL);
   EXPECT_EQ(42, file->Length());
   delete file;
 }
 
 
 UNIT_TEST_CASE(FilePosition) {
   char buf[42];
   const char* kFilename =
       GetFileName("runtime/tests/vm/data/fixed_length_file");
-  File* file = File::Open(kFilename, false);
+  File* file = File::Open(kFilename, File::kRead);
   EXPECT(file != NULL);
   EXPECT(file->ReadFully(buf, 12));
   EXPECT_EQ(12, file->Position());
   EXPECT(file->ReadFully(buf, 6));
   EXPECT_EQ(18, file->Position());
   delete file;
 }