The changes to the WebView are purely about the rendering engine (and possibly javascript engine). The API itself hasn't changed, as any old app will use the new WebView as well.
The actual rendering engine change is from a generic WebKit to that of Blink, used in Chromium. Chrome the application is then a rebranded Chromium, which compared to the WebView, has a lot of its own code separate from the WebView.
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The changes to the WebView are purely about the rendering engine (and possibly javascript engine). The API itself hasn't changed, as any old app will use the new WebView as well.
The actual rendering engine change is from a generic WebKit to that of Blink, used in Chromium. Chrome the application is then a rebranded Chromium, which compared to the WebView, has a lot of its own code separate from the WebView.