[windows] Make most file_win.cc functions use malloc for string conversions.

runtime/bin/utils_win.h

 // 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.
 
 #ifndef BIN_UTILS_WIN_H_
 #define BIN_UTILS_WIN_H_
 
 #include "platform/globals.h"
 
 namespace dart {
@@ skipping 19 matching lines @@
                              intptr_t* result_len = NULL);
   static const wchar_t* Utf8ToWide(const char* utf8,
                                    intptr_t len = -1,
                                    intptr_t* result_len = NULL);
 
  private:
   DISALLOW_ALLOCATION();
   DISALLOW_IMPLICIT_CONSTRUCTORS(StringUtilsWin);
 };
 
+// These scopes provide strings converted as indicated by the scope names.
+// The provided strings are allocated with 'new' and have the same lifetime as
+// the scope.
+class WideToUtf8Scope {
+ public:
+  explicit WideToUtf8Scope(const wchar_t* wide) {
+    intptr_t utf8_len = WideCharToMultiByte(
+          CP_UTF8, 0, wide, -1, NULL, 0, NULL, NULL);
+    char* utf8 = new char[utf8_len];
+    WideCharToMultiByte(CP_UTF8, 0, wide, -1, utf8, utf8_len, NULL, NULL);
+    length_ = utf8_len;
+    utf8_ = utf8;
+  }
+
+  ~WideToUtf8Scope() {
+    delete[] utf8_;
+    utf8_ = NULL;
+  }
+
+  char* utf8() const { return utf8_; }
+  intptr_t length() const { return length_; }
+
+ private:
+  intptr_t length_;
+  char* utf8_;
+
+  DISALLOW_ALLOCATION();
+  DISALLOW_IMPLICIT_CONSTRUCTORS(WideToUtf8Scope);
+};
+
+class Utf8ToWideScope {
+ public:
+  explicit Utf8ToWideScope(const char* utf8) {
+    int wide_len = MultiByteToWideChar(CP_UTF8, 0, utf8, -1, NULL, 0);
+    wchar_t* wide = new wchar_t[wide_len];
+    MultiByteToWideChar(CP_UTF8, 0, utf8, -1, wide, wide_len);
+    length_ = wide_len;
+    wide_ = wide;
+  }
+
+  ~Utf8ToWideScope() {
+    delete[] wide_;
+  }
+
+  wchar_t* wide() const { return wide_; }
+  intptr_t length() const { return length_; }
+
+ private:
+  intptr_t length_;
+  wchar_t* wide_;
+
+  DISALLOW_ALLOCATION();
+  DISALLOW_IMPLICIT_CONSTRUCTORS(Utf8ToWideScope);
+};
+
 }  // namespace bin
 }  // namespace dart
 
 #endif  // BIN_UTILS_WIN_H_