[win] Add comments about AnonymousTokenImpersonator

clip_win.cpp

@@ -53,18 +53,30 @@ class Hglobal {
  HGLOBAL m_handle;
 };
 
+
+// From: https://issues.chromium.org/issues/40080988#comment8
+//
+// "Adds impersonation of the anonymous token around calls to the
+// CloseClipboard() system call. On Windows 8+ the win32k driver
+// captures the access token of the caller and makes it available to
+// other users on the desktop through the system call
+// GetClipboardAccessToken(). This introduces a risk of privilege
+// escalation in sandboxed processes. By performing the
+// impersonation then whenever Chrome writes data to the clipboard
+// only the anonymous token is available."
+//
 class AnonymousTokenImpersonator {
 public:
  AnonymousTokenImpersonator()
- : must_revert(ImpersonateAnonymousToken(GetCurrentThread()))
+ : m_must_revert(ImpersonateAnonymousToken(GetCurrentThread()))
  {}
 
  ~AnonymousTokenImpersonator() {
- if (must_revert)
+ if (m_must_revert)
  RevertToSelf();
  }
 private:
- const bool must_revert;
+ const bool m_must_revert;
 };
 
 }
@@ -87,7 +99,7 @@ lock::impl::impl(void* hwnd) : m_locked(false) {
 
 lock::impl::~impl() {
  if (m_locked) {
- AnonymousTokenImpersonator guard{};
+ AnonymousTokenImpersonator guard;
  CloseClipboard();
  }
 }