Add truncate operation to File API.

runtime/bin/file_win.cc

Index: runtime/bin/file_win.cc
diff --git a/runtime/bin/file_win.cc b/runtime/bin/file_win.cc
index b7454c59bcf8c81a1450227fa805829533b7fa94..8e4e3c14bcee9ddd4522ede070ca24165ff1745e 100644
--- a/runtime/bin/file_win.cc
+++ b/runtime/bin/file_win.cc
@@ -69,9 +69,15 @@ off_t File::Position() {
 }
 
 
-off_t File::SetPosition(int64_t position) {
+bool File::SetPosition(int64_t position) {
   ASSERT(handle_->fd() >= 0);
-  return lseek(handle_->fd(), position, SEEK_SET);
+  return (lseek(handle_->fd(), position, SEEK_SET) != -1);
+}
+
+
+bool File::Truncate(int64_t length) {
+  ASSERT(handle_->fd() >= 0);
+  return (chsize(handle_->fd(), length) != -1);
 }