When the inspector actor walks the DOM in order to find nodes to be
displayed in the inspector panel, it ignores text nodes that contain
only whitespace characters (in order to avoid cluttering the panel with
useless information).
This commit changes this logic so that whitespace text nodes are only
ignored when the node in fact has no layout at all (all text collapsed).
Inside inline formatting contexts, whitespace text nodes may have layout
and therefore push elements further apart. So seeing these nodes in the
panel actually help debugging issues.
MozReview-Commit-ID: GvNMsqsT3w6
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extra : rebase_source : 5c04eaf9e19e952d9f6ca267ef835e1846bc7f4a