We may not want to change common code, but in EFL port, we should be using only one flag for accelerated compositing. I propose to use WTF_USE_COORDINATED_GRAPHICS instead of the various flags we have.
If eliminating build flags are not possible we should at least explicitly mark unsupported combination of flags. As an example if USE_COORDINATED_GRAPHICS is set but ACCELERATED_COMPOSITING is not set for the EFL port the build should explicitly fail (e.g. with an #error msg).
I think it's good to follow Laszlo's suggestion. We inherited Qt's COORDINATED_GRAPHICS. Qt use ACCELERATED_COMPOSITING, TEXTURE_MAPPER, and COORDINATED_GRAPHICS flags by default. COORDINATED_GRAPHICS internally use TEXTURE_MAPPER by default. So another flags like TEXTURE_MAPPER also have to be enable for using COORDINATED_GRAPHICS.
Closing this bug because the EFL port has been removed from trunk. If you feel this bug applies to a different upstream WebKit port and was closed in error, please either update the title and reopen the bug, or leave a comment to request this.