EGL contexts don't need locking, so their Lock and Unlock methods
are empty. Remove them and add them where necessary instead.
Signed-off-by: Elias Naur <mail@eliasnaur.com>
Instead of calling from the low level context into the window
for its surface and dimensions, add a Context.MakeCurrent method
that does it directly.
The result is simpler and clearer logic. For example, synchronization
is obviously no longer needed. It wasn't necessary before, but the
reason was unclear.
Signed-off-by: Elias Naur <mail@eliasnaur.com>