Chrome从V39版本开始不默许支持unity3d webplayer插件

要想启用，需要手动在Chrome浏览器中输入以下命令开启
chrome://flags/#enable-npapi

援引Chrome官方博客的一片文章来解释下Chrome与unity3d webplayer插件默认不兼容的原因：

The Final Countdown for NPAPI

Posted: Monday, November 24, 2014

Last September we announced our plan to remove NPAPI support from Chrome, a change that will improve Chrome’s security, speed, and stability as well as reduce complexity in the code base. Since our last update, NPAPI usage has continued its decline. Given this usage data, we will continue with our deprecation plan.

Monthly Plug-in Launch Percentage

Currently Chrome supports NPAPI plugins, but they are blocked by default unless the user chooses to allow them for specific sites (via the page action UI). A small number of the most popular plugins are whitelisted and allowed by default. In January 2015 we will remove the whitelist, meaning all plugins will be blocked by default.

In April 2015 NPAPI support will be disabled by default in Chrome and we will unpublish extensions requiring NPAPI plugins from the Chrome Web Store. Although plugin vendors are working hard to move to alternate technologies, a small number of users still rely on plugins that haven’t completed the transition yet. We will provide an override for advanced users (via chrome://flags/#enable-npapi) and enterprises (via Enterprise Policy) to temporarily re-enable NPAPI while they wait for mission-critical plugins to make the transition.

In September 2015 we will remove the override and NPAPI support will be permanently removed from Chrome. Installed extensions that require NPAPI plugins will no longer be able to load those plugins.

For more details on the timeline, including guidance for NPAPI plugin developers, see the NPAPI deprecation guide. With each step in this transition, we get closer to a safer, more mobile-friendly web.