Recently Google has published an independently updated version of the Android system component "WebView" in Play Store ( https://play.google.com/store/apps/details?id=com.google.android.webview ). This enables us to update the system's embedded Chromium without re-flashing the whole ROM. For more information about what WebView is, why an independent version, click on the Play Store link.

Unfortunately, this independent version of WebView does not take effect on AOSP-based ROMs (third-party ROMs or non-Nexus factory ROMs) due to a limitation set by the system. This module makes the system automatically use Google's version of WebView instead of the embedded one. Notice that this module only works on Lollipop or later as the independent WebView itself supports only Lollipop and later.

How does it work?
From Lollipop, there is an internal variable in Android named "config_webViewPackageName" which points to the default WebView package (in AOSP it is "com.android.webview"). This module replaces it with "com.google.android.webview" just as what it is in Google's official Android ROMs.

Why not support KitKat/JellyBean/ICS?
It is possible to support KitKat, but it needs more hacking and needs the Google package to support KK (unfortunately it does not).
On pre-KK devices, it is not even possible.