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

runtime/bin/file.h

Index: runtime/bin/file.h
diff --git a/runtime/bin/file.h b/runtime/bin/file.h
index cef6f0a56594ce645dfadce15ba269ec8ada5b68..aa37ba57d08972c6b9f65de8916ff9c4969fb3ed 100644
--- a/runtime/bin/file.h
+++ b/runtime/bin/file.h
@@ -157,15 +157,8 @@ class File : public ReferenceCounted<File> {
   // reading and writing. If mode contains kWrite and the file does
   // not exist the file is created. The file is truncated to length 0 if
   // mode contains kTruncate. Assumes we are in an API scope.
-  static File* ScopedOpen(const char* path, FileOpenMode mode);
-
-  // Like ScopedOpen(), but no API scope is needed.
   static File* Open(const char* path, FileOpenMode mode);
 
-  // Caution! On Windows, the static functions below may call
-  // Dart_ScopeAllocate() to do string conversions! If you call these functions
-  // without a scope, they will fail on Windows!
-
   // Create a file object for the specified stdio file descriptor
   // (stdin, stout or stderr).
   static File* OpenStdio(int fd);
@@ -181,15 +174,17 @@ class File : public ReferenceCounted<File> {
   static int64_t LengthFromPath(const char* path);
   static void Stat(const char* path, int64_t* data);
   static time_t LastModified(const char* path);
-  static const char* LinkTarget(const char* pathname);
   static bool IsAbsolutePath(const char* path);
-  static const char* GetCanonicalPath(const char* path);
   static const char* PathSeparator();
   static const char* StringEscapedPathSeparator();
   static Type GetType(const char* path, bool follow_links);
   static Identical AreIdentical(const char* file_1, const char* file_2);
   static StdioHandleType GetStdioHandleType(int fd);
 
+  // LinkTarget and GetCanonicalPath may call Dart_ScopeAllocate.
+  static const char* LinkTarget(const char* pathname);
+  static const char* GetCanonicalPath(const char* path);
+
   static FileOpenMode DartModeToFileMode(DartFileOpenMode mode);
 
   static CObject* ExistsRequest(const CObjectArray& request);