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

runtime/bin/utils_win.h

Index: runtime/bin/utils_win.h
diff --git a/runtime/bin/utils_win.h b/runtime/bin/utils_win.h
index fe0fa5c814069cdc1ae1ad04ef6de085f1544098..3e7fa4c982e4e535b8047149ffe0a093a8189ebb 100644
--- a/runtime/bin/utils_win.h
+++ b/runtime/bin/utils_win.h
@@ -37,6 +37,61 @@ class StringUtilsWin {
   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