Sunspider : performance of 3rd party apps relative to stock browser
As I mentioned in the comments the Twitter app doesn't seen to have an in-app browser so I'm using the Reddit Is Fun app instead since I know it does. I think that all in-app browsing uses a WebView so it should be the same across all apps. The WebView and Chrome both use the WebKit engine but Chrome seems to use a more up-to-date one. I tried out SunSpider on a few different devices and on the S2 with the Browser. 

Nexus 7

Running Android 4.2.2, Chrome 26.0.1410.58
Chrome: 1747ms (WebKit 537.31)
In-app: 1720ms (WebKit 534.30)


Nexus S

Running Android 4.1.2, Chrome 18.0.1025.166, 
Chrome: 3443.7ms (WebKit 535.19)
In-app: 4307.1ms (WebKit 534.30)


Samgsung Galaxy S2

Running Android 4.1.1 Resurrection Remix v3.8 ROM.
Browser: 1488.8ms (WebKit 534.30)
In-app: 1614.2ms (WebKit 534.30)


I ran the tests twice as I was suprised at the speed of the Galaxy S2 compared to the Nexus 7 but got roughly the same figures.