Add base::mac::ScopedMachPort::release().

Most of our other existing scopers have this method. It allows the scoper to
"give up" its ownership claim.

R=thakis@chromium.org, thakis

Review URL: https://codereview.chromium.org/295933017

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@272956 0039d316-1c4b-4281-b951-d872f2087c98

base/mac/scoped_mach_port.h

@@ -9,6 +9,7 @@
 
 #include "base/base_export.h"
 #include "base/basictypes.h"
+#include "base/compiler_specific.h"
 
 namespace base {
 namespace mac {
@@ -32,6 +33,12 @@ class BASE_EXPORT ScopedMachPort {
     return port_;
   }
 
+  mach_port_t release() WARN_UNUSED_RESULT {
+    mach_port_t temp = port_;
+    port_ = MACH_PORT_NULL;
+    return temp;
+  }
+
  private:
   mach_port_t port_;