Add ScopedObjCClassSwizzler in base/mac, absorbs objc_method_swizzle and ScopedClassSwizzler

base/test/scoped_class_swizzler_mac.h

+// Copyright 2014 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_TEST_SCOPED_CLASS_SWIZZLER_MAC_H_
+#define BASE_TEST_SCOPED_CLASS_SWIZZLER_MAC_H_
+
+#import <objc/runtime.h>
+
+#include "base/macros.h"
+
+namespace base {
+
+// Within a given scope, replace the selector |selector| on |target| with that

[Robert Sesek, 2014/07/21 15:59:01]

We have this code also in //chrome/common/mac/objc_method_swizzle.h in a
namespace called ObjcEvilDoers.

You'll need mark@ for OWNERS approval, so he may have naming ideas, but perhaps
this should be in base::mac::, base::test::, or base::subtle::.

It'd also be nice to consolidate the code.

[Mark Mentovai, 2014/07/21 16:09:58]

rsesek wrote:
I agree, please do this in base/mac and namespace base::mac so that we can
combine this with the existing code we have to do the same thing.

[tapted, 2014/07/22 12:53:49]

Done. I've merged the implementations. Or, more accurately, replaced the older
objc_method_swizzle.* with scoped_objc_class_swizzler.* after incpororating some
things and stealing (and extending) its unit test.

It's a bit of an overhaul - I tried to make a diff in patchset 5 "everything but
the file moves" to paint a better picture of what changed (to the unit test, and
versus patchset 4 to ScopedClassSwizzler). i.e. the diff patchset 5 vs 4 should
show what's changed still.

The two swizzlers were bit different: objc_method_swizzle exchanges methods with
different selectors on the same class implementation; scoped_objc_class_swizzler
exchanges methods with the same selectors on different class implementations. I
think the latter is more robust, and it makes
ObjcEvilDoers::GetImplementedInstanceMethod() redundant, so that part is gone.

I've also made the usage in chrome_browser_application_mac.mm "scoped", where it
wasn't previously. I think it should still outlive anything we care about. I
could also just leak it with a CR_DEFINE_STATIC_LOCAL or similar (keeping it in
anonymous::SwizzleInit()). Let me know what you think.

[Robert Sesek, 2014/07/22 13:59:21]

Yes, I like the Donor pattern.
I think I'd prefer the NSException swizzler to be a CR_DEFINE_STATIC_LOCAL, just
in case any NSExceptions are thrown during shutdown.

[tapted, 2014/07/22 23:41:44]

Done.

+// from |source|.
+class ScopedClassSwizzler {

[Mark Mentovai, 2014/07/21 16:09:58]

This should say ObjC in its name, and the filename should change as a result.
(scoped_objc_class_swizzler_mac.h?)

[tapted, 2014/07/22 12:53:49]

Done (but dropped the _mac - seems more consistent with other files in base/mac)

+ public:
+  ScopedClassSwizzler(Class target, Class source, SEL selector);
+  ~ScopedClassSwizzler();
+
+ private:
+  Method old_selector_impl_;
+  Method new_selector_impl_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedClassSwizzler);
+};
+
+}  // namespace base
+
+#endif  // BASE_TEST_SCOPED_CLASS_SWIZZLER_MAC_H_