Fallback to mediump precision for device that doesn't support highp

[garyyeap]

Tested on Nexus 7 2012 http://chromium-bugs.chromium.narkive.com/XAitJUY1/issue-245755-in-chromium-webgl-regression-highp-precision-is-not-supported-in-fragment-shader

[soliton4]

@garyyeap hi and thank you very much for contributing. i had some changes done to the canvas object which resulted in a new File YUVCanvas.js it replaces the old webglcanvas file.

unfortunately i didnt have it checked in when you did your pr. so could you please redo your changes in the new file?

thank you very much

[garyyeap]

@soliton4 No problem

[Esser50K]

Were these changes ever included?

[soliton4]

@Esser420 i dont think so ...