Improve how we detect that a post has been edited

[Tug]

Currently we detect if a post is modified by checking if the resulting html changed:

See:
#225
#242
#264

We'd like to improve on that logic and reuse the isEditedPostDirty selector from the gutenberg store.

However there are a few road blocks along the way:

• parse and serialize of blocks isn't always symmetric. For instance:

> serialize( parse( `<!-- wp:heading {"align":"center"} -->
<h2 style="text-align:center;">Welcome to Gutenberg!</h2>
<!-- /wp:heading -->` ) )
`<!-- wp:heading {"align":"center"} -->
<h2 style="text-align:center">Welcome to Gutenberg!</h2>
<!-- /wp:heading -->`

(notice the ; at the end of text-align:center)

• Some blocks are updated when the post loads. For instance paragraph and heading both use the RichText component and modify the attributes in onContentSizeChange. But onContentSizeChange is called on load by RCTAztecView (RichText underline component).

[koke]

Is this the same issue than #227?

[Tug]

Yes, it's very close. I suggest we close #227 though as we don't use a hash anymore to check that something has changed

[SergioEstevao]

@Tug is this something that we still want to pursue?

[hypest]

We'd still want to have a performant way of checking for content dirtiness so, marking this as an enhancement and adding it to the Backlog.