webgl: Convert non-raw TexImage sources to the requested format.

The code was returning RGBA8 data from the non-raw sources (HTML
canvas elements, JS ImageData, etc.), but we then validated and passed
that rgba8 data as if it was whatever format/datatype was specified in
TexImage2D/TexSubImage2D, so the pixels would come out as garbage.

It would seem like we could just rewrite the passed in format/datatype
for the TexImage call to be RGBA/UNSIGNED_BYTE, but that would leave
incorrect levels of precision if the internalformat didn't match the
format/datatype (and older desktop implementations often ignore the
internalformat in choosing their internal format, anyway).

components/script/lib.rs

@@ -32,6 +32,7 @@ extern crate audio_video_metadata;
 #[macro_use]
 extern crate bitflags;
 extern crate bluetooth_traits;
+extern crate byteorder;
 extern crate canvas_traits;
 extern crate caseless;
 extern crate cookie as cookie_rs;