Implement pepper flash fullscreen on Mac

ui/base/cocoa/underlay_opengl_hosting_window.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/underlay_opengl_hosting_window.h"
+
+#include "base/logging.h"
+
+@implementation UnderlayOpenGLHostingWindow
+
+- (void)underlaySurfaceAdded {
+  DCHECK_GE(underlaySurfaceCount_, 0);
+  ++underlaySurfaceCount_;
+
+  // We're having the OpenGL surface render under the window, so the window
+  // needs to be not opaque.
+  if (underlaySurfaceCount_ == 1)
+    [self setOpaque:NO];
+}
+
+- (void)underlaySurfaceRemoved {
+  --underlaySurfaceCount_;
+  DCHECK_GE(underlaySurfaceCount_, 0);
+
+  if (underlaySurfaceCount_ == 0)
+    [self setOpaque:YES];
+}
+
+@end