Add an instrument option to disable generation of native block bodies

[macournoyer]

Problem

As mentioned in #80 (comment), currently all shops profiled through the Theme Inspector don't see the profiling of the section templates.

(This should be 6 levels deep)

Solution

We need a way to disable generation of native BlockBody::C when profiling will happen later, but don't want to profile yet.

The new option is to be used here: https://github.com/Shopify/storefront-renderer/blob/master/app/liquid/theme_render_context.rb#L265-L269

The name was to imply parse this for profiling (instrument it), but don't profile it. I imagined in the future, it will mean: generate byte-code that is instrumented. But opened to suggestions on the name.

[macournoyer]

Setting profile: true for the section template's ParseContext cause a nil exception on line https://github.com/Shopify/liquid/blob/master/lib/liquid/profiler.rb#L90. I tried fixing that, but that didn't solve the issue of section profiling not showing up. So this seems like the simplest solution to buy some time before introducing profiling in the VM.

[dylanahsmith]

This sounds like it might be an application specific issue, since it has to do with sections and not just the include/render tag.

It sounds like the intent of the instrument: true option is the same as the profile: true parse, which is to parse the template for profiling.

I think we could just name the option :disable_liquid_c_nodes which could be useful more generally, such as to use liquid parse tree.

[macournoyer]

Done. Will add a TODO in SFR code to remove it once liquid-c gets profiling support.