This relatively old webpage[1] talks about the possibility of side channel attacks in javascript(among other things).I believe this applies to Phonegap.
Thank you, these sorts of timing attacks are very interesting. I was asking for clarification because I am curious about vectors such as these; vulnerabilities in JS runtime or in HTML/CSS. This thinking was spurred by an article posted here not to long ago[1] about timing attacks on CSS and SVG shaders through requestAnimationFrame.
[1] http://www.contextis.com/files/Browser_Timing_Attacks.pdf