Added booleans that indicate which GL extensions are available.

Added booleans that indicate which GL extensions are available.

This is because some implementations of eglGetProcAddress do not return null for entry points that are not available. This gives a convenient and efficient way of determining whether a particular entry point can be called.
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=108153

[Ken Russell (switch to Gerrit), 2011-10-29 01:48:07]

LGTM

I'm pretty sure that there are other places in the code where we assume that the
OpenGL function names are actually function pointers, and where we should be
checking for the extension instead. Any idea how we could track all of these
down? Or to avoid using them in this way?

[apatrick_chromium, 2011-11-01 18:19:15]

Yeah I was thinking about how to find them all. I could change the binding
macros from

#define glClearColor gfx::g_glClearColor

to

#define glClearColor(r, g, b, a) gfx::glClearColor(r, g, b, a)

Then failing to specify the arguments would be a preprocessor error. There might
still be some legit reasons to bind to the function pointers directly though,
perhaps in skia.