[GLES2] Perfomance Regression in rendering some shader on iOS

To Reproduce:

1. Build and run the attached project on iOS with GLES2 (tested on an iPad Air 1 iOS 9.0 & iOS 8.2) with Unity 5.4 and UNity 5.1.
2. Observe that it takes much more time to render the scene on 5.4 (it only has 15 cubes with an identical shader).

5.4
GPU frametime: 4.3ms
5.1:
GPU frametime: 1.6ms

This is not reproducble on Metal (there is a ~1.5ms difference, but it's caused by an extra blit introduced by mt rendering, so probably not related to this)

I've also attached GPU stacktraces here.

Split from this case https://fogbugz.unity3d.com/default.asp?761024 because Metal issues have been mostly resolved and remaining regression in Metal seem to be caused by an mt rendering issue.

Tested with:

Version 5.4.0b5 (3ef12c3e0f69)
Mon, 25 Jan 2016 05:53:46 GMT
Branch: 5.4/release

and

5.1.4f1