[Mac] Allow NSExceptions in certain cases.

base/mac/scoped_nsexception_enabler.h

+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_MAC_SCOPED_NSEXCEPTION_ENABLER_H_
+#define BASE_MAC_SCOPED_NSEXCEPTION_ENABLER_H_
+#pragma once
+
+#include "base/basictypes.h"
+
+namespace base {
+namespace mac {
+
+// ChromeBrowserApplication attempts to restrict throwing of
+// NSExceptions because they interact badly with C++ scoping rules.
+// Unfortunately, there are some cases where exceptions must be
+// supported, such as when third-party printer drivers are used.
+// These helpers can be used to enable exceptions for narrow windows.
+
+// Make it easy to safely allow NSException to be throw in a limited
+// scope.  Note that if an exception is throw, then this object will
+// not be appropriately destructed!  If the exception ends up in the
+// top-level event loop, things are cleared in -reportException:.  If
+// the exception is caught at a lower level, a higher level scoper
+// should eventually reset things.
+class ScopedNSExceptionEnabler {
+ public:
+  // Passing |true| enables exceptions within this scope, passing
+  // |false| leaves the current setting alone.  This allows optionally
+  // enabling exceptions without requiring contrived code (like using
+  // |scoped_ptr<ScopedNSExceptionEnabler>|).
+  ScopedNSExceptionEnabler(bool enable);
+  ~ScopedNSExceptionEnabler();
+
+ private:
+  bool was_enabled_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedNSExceptionEnabler);
+};
+
+// Access the exception setting for the current thread.  This is for
+// the support code in ChromeBrowserApplication, other code should use
+// the scoper.
+bool GetNSExceptionsAllowed();
+void SetNSExceptionsAllowed(bool allowed);
+
+}  // namespace mac
+}  // namespace base
+
+#endif BASE_MAC_SCOPED_NSEXCEPTION_ENABLER_H_