We need NEON detection for ARMv7 platforms like the Tegra2 which do not have NEON support, similar to the detection that already exists for SSE, etc., on x86. Currently, we have detection in pixman, libtheora, libvpx, and jstracer, at the very least. Bug 620526 also added a custom version for YUV2RGB code (which was broken, fixed in bug 637961). We can't do much about the 3rd-party libraries, since they have to work outside of the Mozilla tree, but we should at least centralize our own detection. The "Add ScaleYCbCrToRGB565" patch in bug 634557 adds such generic detection. I'm breaking it out into this bug for the purposes of tracking and review.

The code in the attached patch is based on the libtheora/libvpx code (which I wrote). It has been tested on both Maemo and Android, and x86 Linux, and does the right thing in each case. I have not yet tested it on a Tegra2, because I don't have one.

Apparently this is a duplicate of 583958 (I searched, but failed to find it before; thanks to dbaron for pointing it out).