Make common utility to load views from nibs.

ui/base/cocoa/nib_loading.mm

+// Copyright (c) 2012 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 "ui/base/cocoa/nib_loading.h"
+
+#include "base/mac/bundle_locations.h"
+#include "base/memory/scoped_nsobject.h"
+
+namespace ui {
+
+NSView* GetViewFromNib(NSString* name) {
+  scoped_nsobject<NSNib> nib(
+      [[NSNib alloc] initWithNibNamed:name
+                               bundle:base::mac::FrameworkBundle()]);
+  if (!nib)
+    return nil;
+
+  NSArray* objects;
+  BOOL success = [nib instantiateNibWithOwner:nil
+                              topLevelObjects:&objects];
+  if (!success)
+    return nil;
+
+  // When loading a nib manually (as opposed to using an NSWindowController or
+  // NSViewController), all the top-level objects need to be explicitly
+  // released. See
+  // http://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/LoadingResources/CocoaNibs/CocoaNibs.html#//apple_ref/doc/uid/10000051i-CH4-SW10
+  // for more information.
+  [objects makeObjectsPerformSelector:@selector(release)];
+
+  // For some strange reason, even nibs that appear to have but one top-level
+  // object often have more (an NSApplication, etc.). Filter out what isn't
+  // desired.
+  for (NSView* view in objects) {
+    if (![view isKindOfClass:[NSView class]])
+      continue;
+
+    return [[view retain] autorelease];
+  }
+
+  return nil;
+}
+
+}  // namespace ui