[Mac] Allow NSExceptions in certain cases.

Thirdy-party print drivers seem to be a source of NSExceptions which
Chromium will never be able to fix.  ScopedNSExceptionEnabler causes
the code which makes throwing an NSException fatal to allow throws.
The flag will be reset in -reportException: in most cases.

For now, allow exceptions to be thrown for -selectPDE: (bug 80686) and
PrintingContextMac::AskUserForSettings() (bug 82589).

BUG=80686, 82589
TEST=Monitor crash server.


Review URL: http://codereview.chromium.org/7038010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@86503 0039d316-1c4b-4281-b951-d872f2087c98

3 files changed, 92 insertions, 0 deletions

diff --git a/base/base.gypi b/base/base.gypi
index c3bcd00..22d66f8 100644
--- a/base/base.gypi
+++ b/base/base.gypi
@@ -129,6 +129,8 @@
           'mac/scoped_cftyperef.h',
           'mac/scoped_nsautorelease_pool.h',
           'mac/scoped_nsautorelease_pool.mm',
+          'mac/scoped_nsexception_enabler.h',
+          'mac/scoped_nsexception_enabler.mm',
           'mach_ipc_mac.h',
           'mach_ipc_mac.mm',
           'memory/linked_ptr.h',
diff --git a/base/mac/scoped_nsexception_enabler.h b/base/mac/scoped_nsexception_enabler.h
new file mode 100644
index 0000000..a10120b
--- /dev/null
+++ b/base/mac/scoped_nsexception_enabler.h
@@ -0,0 +1,46 @@
+// 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 {
+
+// BrowserCrApplication 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 thrown in a limited
+// scope.  Note that if an exception is thrown, 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:
+  ScopedNSExceptionEnabler();
+  ~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 BrowserCrApplication, other code should use
+// the scoper.
+bool GetNSExceptionsAllowed();
+void SetNSExceptionsAllowed(bool allowed);
+
+}  // namespace mac
+}  // namespace base
+
+#endif  // BASE_MAC_SCOPED_NSEXCEPTION_ENABLER_H_
diff --git a/base/mac/scoped_nsexception_enabler.mm b/base/mac/scoped_nsexception_enabler.mm
new file mode 100644
index 0000000..6815de3
--- /dev/null
+++ b/base/mac/scoped_nsexception_enabler.mm
@@ -0,0 +1,44 @@
+// 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.
+
+#import "base/mac/scoped_nsexception_enabler.h"
+
+#import "base/lazy_instance.h"
+#import "base/threading/thread_local.h"
+
+// To make the |g_exceptionsAllowed| declaration readable.
+using base::LazyInstance;
+using base::LeakyLazyInstanceTraits;
+using base::ThreadLocalBoolean;
+
+namespace {
+
+// Whether to allow NSExceptions to be raised on the current thread.
+LazyInstance<ThreadLocalBoolean, LeakyLazyInstanceTraits<ThreadLocalBoolean> >
+    g_exceptionsAllowed(base::LINKER_INITIALIZED);
+
+}  // namespace
+
+namespace base {
+namespace mac {
+
+bool GetNSExceptionsAllowed() {
+  return g_exceptionsAllowed.Get().Get();
+}
+
+void SetNSExceptionsAllowed(bool allowed) {
+  return g_exceptionsAllowed.Get().Set(allowed);
+}
+
+ScopedNSExceptionEnabler::ScopedNSExceptionEnabler() {
+  was_enabled_ = GetNSExceptionsAllowed();
+  SetNSExceptionsAllowed(true);
+}
+
+ScopedNSExceptionEnabler::~ScopedNSExceptionEnabler() {
+  SetNSExceptionsAllowed(was_enabled_);
+}
+
+}  // namespace mac
+}  // namespace base