Backend pieces of auto-update enable/disable

[humphd]

This updates Brackets for the API changes necessary for https://github.com/mozilla/thimble.mozilla.org/issues/1417.

There are 2 types of "reloads" that we do. The first is a full reload for cases where the DOM needs to be altered in a way that can't be done easily, which is like refreshing the browser tab. The second is a dynamic injection of content that doesn't warrant a full reload. For example, updating the text in a paragraph tag.

This patch makes it possible to stop the first kind of reload, which is what I think we want. If we decide that we also want to stop the second type, it's going to be hacky. I would need to inspect messages going over the LiveDev transport, and look for things like "_LD.applyDOMEdits([{"type":"textReplace"... deep inside the string of a Runtime.evaluate message. I could do this, but if I don't have to, I'd rather not.

cc @flukeout
r? @gideonthomas

[humphd]

It looks like if I want to do 2), I could also try to prevent it at the source, which is https://github.com/mozilla/brackets/blob/master/src/LiveDevelopment/MultiBrowserImpl/documents/LiveHTMLDocument.js#L212-L229, specifically line 221. I'd just need to wrap this in a guard that can be enabled/disabled via the Bramble client.

[humphd]

One thing to consider here: our highlighting code depends on the DOM being a) up-to-date such that b) DOM nodes referenced in the editor actually exist in the preview. If the editor and preview are allowed to drift out of sync dramatically, the highlighting code is going to get more and more unusable, as new additions to the editor cease to appear in the preview.

[gideonthomas]

I don't think we should support the second case. From what I understand, the issue was that it was annoying that the preview was flickering because of a full refresh (the first case). So allowing a toggle on that should be fine. Toggling live dev based on LiveDocuments might be overkill. I think we we make it clear in the UI that should be fine.

As for the highlighting code, we can force a reload (which should sync DOM elements) when it is toggled, can't we?

[gideonthomas]

The patch itself lgtm! r+

[flukeout]

Okay, I'm going to start work on a companion PR in Thimble to match this effort. Will holler if I run into problems.

[humphd]

@flukeout I'm going to land this. If we decide to change the disabled state to also block dynamic injection, we can do it in a new patch. I think that @gideonthomas is right, we probably don't want it.

[flukeout]

@humphd okay perfect, PR incoming for the toggle later today