[MacViews] Implement colored window frames.

chrome/browser/ui/cocoa/apps/scoped_fake_nswindow_main_status.mm

+// Copyright 2015 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 "chrome/browser/ui/cocoa/apps/scoped_fake_nswindow_main_status.h"
+
+#import <Cocoa/Cocoa.h>
+
+#import "base/mac/foundation_util.h"
+
+// Donates a testing implementation of [NSWindow isMainWindow].
+@interface IsMainWindowDonorForWindow : NSObject
+@end
+
+@implementation IsMainWindowDonorForWindow
+- (BOOL)isMainWindow {
+  NSWindow* selfAsWindow = base::mac::ObjCCastStrict<NSWindow>(self);
+  return selfAsWindow == ScopedFakeNSWindowMainStatus::GetMainWindow();
+}
+@end
+
+NSWindow* ScopedFakeNSWindowMainStatus::window_ = nil;
+
+ScopedFakeNSWindowMainStatus::ScopedFakeNSWindowMainStatus(NSWindow* window)
+    : swizzler_([NSWindow class],
+                [IsMainWindowDonorForWindow class],
+                @selector(isMainWindow)) {
+  DCHECK(!window_);
+  window_ = window;
+}
+
+ScopedFakeNSWindowMainStatus::~ScopedFakeNSWindowMainStatus() {
+  window_ = nil;
+}