Auto merge of #2593 - fschutt:granular_debug_render_feature, r=kvark
Auto merge of #2593 - fschutt:granular_debug_render_feature, r=kvark

Make the debug_renderer feature more granular (fix for #2574)

Should resolve Gecko issues. The feature `capture` doesn't need access to all the struct necessary for the feature `debug_renderer`, just some functions from `device.rs` were disabled.

This PR includes #2591, not sure how they could be merged together.

/r? @kvark

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servo/webrender,servo/webrender,servo/webrender,servo/webrender,servo/webrender,servo/webrender