[gardening] Fix gen_snapshot crash on msvc.

Revert change to StringRAII which used to take reference, but was changed to take pointer in 2ead86a

Fixes #49978
TEST=ci

Change-Id: I8d8b18e6e9ae3cd07427ee1b37df404d11dcb26e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/260402
Commit-Queue: Alexander Aprelev <[email protected]>
Reviewed-by: Liam Appelbe <[email protected]>

Author: aam

runtime/bin/file_win.cc

@@ -323,9 +323,9 @@ File* File::OpenFD(int fd) {
 
 class StringRAII {
  public:
-  explicit StringRAII(StringRAII* origin) {
-    own_ = origin->own_;
-    s_ = origin->release();
+  explicit StringRAII(StringRAII& origin) {  // NOLINT
+    own_ = origin.own_;
+    s_ = origin.release();
   }
 
   explicit StringRAII(const char* s) : s_(s), own_(false) {}