WebKit's WebGL implementation isn't advertising EXT_color_buffer_half_float on iOS (at least the simulator, and almost surely hardware too). FP texture renderability used to be implicit in the non-ANGLE backend, but is explicit now. This means that FP16 textures can't be used as FBO attachments. This functionality difference could be the reason for some content not working.
OES_texture_half_float is supported since Bug 210524, and EXT_color_buffer_half float since Bug 210994.
Created attachment 399940 [details]
Note that there are important steps to take when updating ANGLE. See http://trac.webkit.org/wiki/UpdatingANGLE
Committed r261990: <https://trac.webkit.org/changeset/261990>
All reviewed patches have been landed. Closing bug and clearing flags on attachment 399940 [details].